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/text-input-behavior.html

@@ -1,12 +1,12 @@
 <link rel="import" href="text-input-dialog.html">
 <script>
 'use strict';
-window.Chat = window.Chat || {};
+window.Snapdrop = window.Snapdrop || {};
 (function() {
     var textInput = Polymer.Base.create('text-input-dialog');
     textInput.className = 'textInput';
     document.body.appendChild(textInput);
-    Chat.TextInputBehavior = {
+    Snapdrop.TextInputBehavior = {
         properties: {
             contact: Object,
         },