Add unique classes to important alert dialogs to be used for plugin customization.

static/js/controllers/uicontroller.js

@@ -709,12 +709,12 @@ define(['jquery', 'underscore', 'bigscreen', 'moment', 'sjcl', 'modernizr', 'web
 
 		_.defer(function() {
 			if (!Modernizr.websockets) {
-				alertify.dialog.alert(translation._("Your browser is not supported. Please upgrade to a current version."));
+				alertify.dialog.alert(translation._("Your browser is not supported. Please upgrade to a current version."), null, null, 'unsupportedBrowserPleaseUpgrade');
 				$scope.setStatus("unsupported");
 				return;
 			}
 			if (!$window.webrtcDetectedVersion) {
-				alertify.dialog.alert(translation._("Your browser does not support WebRTC. No calls possible."));
+				alertify.dialog.alert(translation._("Your browser does not support WebRTC. No calls possible."), null, null, 'webrtcUnsupportedBrowserNoCalls');
 				return;
 			}
 			if (mediaStream.config.Renegotiation && $window.webrtcDetectedBrowser === "firefox" && $window.webrtcDetectedVersion < 38) {