style: catalog all z-indexes and move toolbar down

All z-indexes found in css files have been moved into css
variables. If the z-index is used only once, the variable
name will be the same as the selector it is used in. If
the z-index is used multiple times, then the plain name
of $zindex# was used. This allowed a more confident
moving down of the toolbar so that the new modal dialog,
with z-index 500, could display on top of it.

#1436

css/_base.scss

     height: 74px;
     background-size: contain;
     background-repeat: no-repeat;
-    z-index: 2;
+    z-index: $zindex2;
 }
 
 .leftwatermark {
     font-size: 11pt;
     color: rgba(255,255,255,.50);
     text-decoration: none;
-    z-index: 100;
+    z-index: $poweredByZ;
 }
 
 .connected {

css/_filmstrip.scss

         flex-direction: column-reverse;
         flex-wrap: nowrap;
         position: relative;
-        z-index: 1;                     // Set z-index to make element visible
+        z-index: $zindex1;              // Set z-index to make element visible
         width: $hideFilmstripButtonWidth;
 
         button {
         bottom: 0;
         width:auto;
         border: $thumbnailsBorder solid transparent;
-        z-index: 5;
+        z-index: $filmstripVideosZ;
         transition: bottom 2s;
         overflow: visible !important;
         /*!!!Removes the gap between the local video container and the remote

css/_jitsi_popover.scss

     position: absolute;
     top: 0;
     left: 0;
-    z-index: 1010;
+    z-index: $jitsipopoverZ;
     display: none;
     max-width: 300px;
     min-width: 100px;

css/_jquery.contextMenu.scss

   position: absolute;
   top: 50%;
   right: 8px;
-  z-index: 1; 
+  z-index: $zindex1;
   width: 0;
   height: 0;
   content: '';

css/_keyboard-shortcuts.scss

     overflow: hidden;
     padding: 20px;
     margin-left: 10px;
-    z-index: 10;
+    z-index: $zindex10;
     border-radius: $borderRadius;
     background-attachment: scroll;
     background-size: auto auto;

css/_notice.scss

 .notice {
     position: relative;
-    z-index: 3;
+    z-index: $zindex3;
     margin-top: 6px;
 
     &__message {

css/_popover.scss

   position: absolute;
   top: 0;
   left: 0;
-  z-index: 1015;
+  z-index: $popoverZ;
   display: none;
   max-width: 300px;
   min-width: 100px;

css/_side_toolbar_container.scss

     position: absolute;
     top: 0;
     width: 0;
-    z-index: 800;
+    z-index: $sideToolbarContainerZ;
 
     /**
      * Labels inside the side panel.

css/_toolbars.scss

 
 #subject {
     position: relative;
-    z-index: 3;
+    z-index: $zindex3;
     width: auto;
     padding: 5px;
     margin-left: 40%;
     height: 50px;
     cursor: pointer;
     text-align: center;
-    z-index: 1;
+    z-index: $zindex1;
     font-size: $toolbarFontSize !important;
     line-height: 50px !important;
     vertical-align: middle;

css/_variables.scss

 /**
  * Z-indexes. TODO: Replace this by a function.
  */
-$tooltipsZ: 901;
-$toolbarZ: 900;
+$zindex0: 0;
+$zindex1: 1;
+$zindex2: 2;
+$zindex3: 3;
+$filmstripVideosZ: 5;
+$zindex10: 10;
+$reloadZ: 20;
+$poweredByZ: 100;
+$ringingZ: 300;
+$sideToolbarContainerZ: 300;
+$toolbarZ: 400;
+$tooltipsZ: 401;
+$dropdownMaskZ: 900;
+$dropdownZ: 901;
 $overlayZ: 902;
+$jitsipopoverZ: 1010;
+$centeredVideoLabelZ: 1011;
 $notificationZ: 1012;
-$ringingZ: 800;
-$dropdownZ: 901;
-$dropdownMaskZ: 900;
+$popoverZ: 1015;
+
 
 /**
  * Font Colors

css/_videolayout_default.scss

     &__toptoolbar {
         position: absolute;
         left: 0;
-        z-index: 3;
+        z-index: $zindex3;
         width: 100%;
         box-sizing: border-box; // Includes the padding in the 100% width.
     }
             float: left;
             @include circle($thumbnailIndicatorSize);
             box-sizing: border-box;
-            z-index: 3;
+            z-index: $zindex3;
             background: $dominantSpeakerBg;
             color: $thumbnailPictogramColor;
             border: $thumbnailIndicatorBorder solid $thumbnailPictogramColor;
         width: 100%;
         height: 100%;
         visibility: hidden;
-        z-index: 2;
+        z-index: $zindex2;
     }
 }
 
     position: absolute;
     left: 0;
     top: 0;
-    z-index: 1;
+    z-index: $zindex1;
     width: 100%;
     height: 100%;
 }
 }
 
 #etherpad {
-    z-index: 0;
+    z-index: $zindex0;
 }
 
 /**
     overflow: hidden;
     white-space: nowrap;
     line-height: $thumbnailToolbarHeight;
-    z-index: 2;
+    z-index: $zindex2;
 }
 
 /**
     padding: 3px 5px;
     font-size: 9pt;
     cursor: pointer;
-    z-index: 2;
+    z-index: $zindex2;
 }
 
 /**
     top: 0px;
     right: 0;
     margin: 7px;
-    z-index: 3;
+    z-index: $zindex3;
     width: 18px;
     height: 13px;
     color: #FFF;
     margin-top: -17px;
     width: 6px;
     height: 35px;
-    z-index: 2;
+    z-index: $zindex2;
     border: none;
 
     .audiodot-top,
     background-clip: padding-box;
     -webkit-border-radius: 5px;
     -webkit-background-clip: padding-box;
-    z-index: 20; /*The reload button should appear on top of the header!*/
+    z-index: $reloadZ; /*The reload button should appear on top of the header!*/
 }
 
 .audiolevel {
     display: inline-block;
     position: absolute;
-    z-index: 0;
+    z-index: $zindex0;
     border-radius:1px;
     pointer-events: none;
 }
 .noMic {
     position: absolute;
     border-radius: 8px;
-    z-index: 1;
+    z-index: $zindex1;
     width: 100%;
     height: 100%;
     background-image: url("../images/noMic.png");
 .noVideo {
     position: absolute;
     border-radius: 8px;
-    z-index: 1;
+    z-index: $zindex1;
     width: 100%;
     height: 100%;
     background-image: url("../images/noVideo.png");
     display: none;
     position: absolute;
     width: auto;
-    z-index: 2;
+    z-index: $zindex2;
     font-weight: 600;
     font-size: 14px;
     text-align: center;
     left: 0;
     width: 100%;
     top:50%;
-    z-index: 2;
+    z-index: $zindex2;
     font-weight: 600;
     font-size: 14px;
     text-align: center;
 #videoResolutionLabel,
 .centeredVideoLabel {
     display: none;
-    z-index: 1011;
+    z-index: $centeredVideoLabelZ;
 }
 
 .centeredVideoLabel {

css/_welcome_page.scss

     font-weight: 500;
     font-size: 16px;
     color: #acacac;
-    z-index: 2;
+    z-index: $zindex2;
 }
 
 #disable_welcome:checked + label
     font-weight: 500;
     font-size: 16px;
     color: #acacac;
-    z-index: 2;
+    z-index: $zindex2;
 }
 
 #enter_room_form {
         float: left;
         background-color: #FFFFFF;
         position: relative;
-        z-index: 2;
+        z-index: $zindex2;
     }
 
     &__reload {
         color: #acacac;
         font-size: 1.9em;
         line-height: 55px;
-        z-index: 3;
+        z-index: $zindex3;
         float:  left;
         cursor: pointer;
         text-align: center;
         outline: none;
         float:left;
         position: relative;
-        z-index: 2;
+        z-index: $zindex2;
     }
 }