Add getSyncToken and setSyncToken to data store interface.

This allows local storage to hold onto the token across page refreshes.

lib/store/stub.js

@@ -5,15 +5,31 @@
  */
 
 /**
- * Construct a stub store. This does no-ops on all store methods.
+ * Construct a stub store. This does no-ops on most store methods.
  * @constructor
  */
 function StubStore() {
-
+    this.fromToken = null;
 }
 
 StubStore.prototype = {
 
+    /**
+     * Get the sync token.
+     * @return {string}
+     */
+    getSyncToken: function() {
+        return this.fromToken;
+    },
+
+    /**
+     * Set the sync token.
+     * @param {string} token
+     */
+    setSyncToken: function(token) {
+        this.fromToken = token;
+    },
+
     /**
      * No-op.
      * @param {Room} room