Updates invitation email.

index.html

     <script src="libs/popover.js?v=1"></script><!-- bootstrap tooltip lib -->
     <script src="libs/pako.bundle.js?v=1"></script><!-- zlib deflate -->
     <script src="libs/toastr.js?v=1"></script><!-- notifications lib -->
-    <script src="interface_config.js?v=4"></script>
+    <script src="interface_config.js?v=5"></script>
     <script src="muc.js?v=17"></script><!-- simple MUC library -->
     <script src="estos_log.js?v=2"></script><!-- simple stanza logger -->
     <script src="desktopsharing.js?v=3"></script><!-- desktop sharing -->
     <script src="local_sts.js?v=2"></script><!-- Local stats processing -->
     <script src="videolayout.js?v=31"></script><!-- video ui -->
     <script src="connectionquality.js?v=1"></script>
-    <script src="toolbar.js?v=6"></script><!-- toolbar ui -->
+    <script src="toolbar.js?v=7"></script><!-- toolbar ui -->
     <script src="toolbar_toggler.js?v=2"></script>
     <script src="canvas_util.js?v=1"></script><!-- canvas drawing utils -->
     <script src="audio_levels.js?v=4"></script><!-- audio levels plugin -->

interface_config.js

     SHOW_POWERED_BY: false,
     GENERATE_ROOMNAMES_ON_WELCOME_PAGE: true,
     APP_NAME: "Jitsi Meet",
+    INVITATION_POWERED_BY: true,
     ACTIVE_SPEAKER_AVATAR_SIZE: 100
 };

toolbar.js

         }
 
         var conferenceName = roomUrl.substring(roomUrl.lastIndexOf('/') + 1);
-        var subject = "Invitation to a Jitsi Meet (" + conferenceName + ")";
-        var body = "Hey there, I%27d like to invite you to a Jitsi Meet" +
+        var subject = "Invitation to a " + interfaceConfig.APP_NAME + " (" + conferenceName + ")";
+        var body = "Hey there, I%27d like to invite you to a " + interfaceConfig.APP_NAME +
                     " conference I%27ve just set up.%0D%0A%0D%0A" +
                     "Please click on the following link in order" +
                     " to join the conference.%0D%0A%0D%0A" +
                     roomUrl +
                     "%0D%0A%0D%0A" +
                     sharedKeyText +
-                    "Note that Jitsi Meet is currently" +
+                    "Note that " + interfaceConfig.APP_NAME + " is currently" +
                     " only supported by Chromium," +
                     " Google Chrome and Opera, so you need" +
                     " to be using one of these browsers.%0D%0A%0D%0A" +
             body += "%0D%0A%0D%0A" + window.localStorage.displayname;
         }
 
+        if (interfaceConfig.INVITATION_POWERED_BY) {
+            body += "%0D%0A%0D%0A--%0D%0Apowered by jitsi.org";
+        }
+
         window.open("mailto:?subject=" + subject + "&body=" + body, '_blank');
     }