Improved FiFo VNC client.

1. isolated the api version in vnc.js
2. make able to give ws host&port in query params.
   This will be not only convenient in dev mode (since grunt proxy mode does not
   proxy ws links, now can manually assign), and also convenient when user
   simply want to connect to other host.
3. I have cleaned the UI a little, added some eye-candy elements.
    Include that fixed the missing style 'alert-error' when can not connect to target.