Rename global variable 'Chat' to 'Snapdrop'

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

app/elements/sound-notification/sound-notification-behavior.html

@@ -1,8 +1,8 @@
 <link rel="import" href="sound-notification.html">
 <script>
 'use strict';
-Chat = window.Chat || {};
-Chat.SoundNotificationBehavior = {
+Snapdrop = window.Snapdrop || {};
+Snapdrop.SoundNotificationBehavior = {
     sounds: function() {
         var sounds = document.querySelector('sound-notification');
         if (!sounds) {