UI bug fixes.

Ran grunt test.

Fixes in this pull request
- Change the title of the extension popup from "uProxy polymer UI" to "uProxy" 
- Instead of closing/reopening the popup each time the popup URL changes, update the URL of the popup. (This prevents a weird flash where the "install app" popup opens, the app connects, and the popup immediately closes.)
- vulcanize Chrome extension Polymer code. 
- fix https://github.com/uProxy/uproxy/issues/716 by checking in the callback of chrome.window.create if the popup url we've just opened has changed since we called create.
and popupWindowId should probably be a private member of this class