Add storeEvents impl.

lib/store/stub.js

@@ -86,6 +86,16 @@ StubStore.prototype = {
      */
     scrollback: function(room, limit) {
         return [];
+    },
+
+    /**
+     * Store events for a room.
+     * @param {Room} room The room to store events for.
+     * @param {Array<MatrixEvent>} events The events to store.
+     * @param {string} token The token associated with these events.
+     * @param {boolean} toStart True if these are paginated results.
+     */
+    storeEvents: function(room, events, token, toStart) {
     }
 
     // TODO