resolutions: add 540p aka qHD

service/RTC/Resolutions.js

     '1080': {
         width: 1920,
         height: 1080,
-        order: 7
+        order: 8
     },
     'fullhd': {
         width: 1920,
         height: 1080,
-        order: 7
+        order: 8
     },
     '720': {
         width: 1280,
         height: 720,
-        order: 6
+        order: 7
     },
     'hd': {
         width: 1280,
         height: 720,
-        order: 6
+        order: 7
     },
     '960': {
         width: 960,
         height: 720,
+        order: 6
+    },
+    '540': {
+        width: 960,
+        height: 540,
+        order: 5
+    },
+    'qhd': {
+        width: 960,
+        height: 540,
         order: 5
     },