Add option to view event source (#320)

* Add view source

* Add view source cons

* Change design

* Use PopupWindow instead of Dialog

* Undo changes to Dialog.jsx

src/client/action/navigation.js

@@ -109,6 +109,13 @@ export function openReadReceipts(roomId, userIds) {
   });
 }
 
+export function openViewSource(event) {
+  appDispatcher.dispatch({
+    type: cons.actions.navigation.OPEN_VIEWSOURCE,
+    event,
+  });
+}
+
 export function replyTo(userId, eventId, body) {
   appDispatcher.dispatch({
     type: cons.actions.navigation.CLICK_REPLY_TO,