Rename global variable 'Chat' to 'Snapdrop'

Initially a lot of code was copied from another project. This lead to confusing naming conventions.

app/elements/text-sharing/clipboard-behavior.html

@@ -8,7 +8,7 @@
     style.top = '-10000px';
     document.body.appendChild(copyTextarea);
 
-    window.Chat.ClipboardBehavior = {
+    window.Snapdrop.ClipboardBehavior = {
         copyToClipboard: function(content) {
             copyTextarea.value = content;
             var range = document.createRange();