Fix embed DOM classes

Classes, IDs and Names in the DOM have to begin with a letter. The $$hashKey
however might not, so prefix it with embed_. This also makes the classes more
unique, which is a good thing. Additionally, don't scroll on undefined should that
ever happen.

Fixes #45

directives/plugin.html

@@ -4,7 +4,7 @@
     Hide {{ plugin.name }}
   </button>
 
-  <div ng-bind-html="displayedContent" bo-class="plugin.$$hashKey"></div>
+  <div ng-bind-html="displayedContent" bo-class="'embed_' + plugin.$$hashKey"></div>
 </div>
 
 <div ng-hide="plugin.visible">

js/glowingbear.js

@@ -813,8 +813,10 @@ weechat.directive('plugin', function() {
 
                 // Scroll embed content into view
                 var scroll = function() {
-                    var embed = document.querySelector("." + $scope.plugin.$$hashKey);
-                    embed.scrollIntoViewIfNeeded();
+                    var embed = document.querySelector(".embed_" + $scope.plugin.$$hashKey);
+                    if (embed) {
+                        embed.scrollIntoViewIfNeeded();
+                    }
                 };
                 setTimeout(scroll, 100);
             };