Handle multiple comma-separated WS protocols (codecs).

Master branch of noVNC project sets WebSocket-Protocol/Sec-WebSocket-Protocol header with multiple comma-separated codecs (binary, base64). Current form will trow error: 
```
Couldn't handle WS protocol binary, base64!
```
This patch will enable iteration through header codecs and will set ```self.codec``` variable to first codec we can encode/decode.

Patch solves "reported bug" using noVNC master branch with Ganeti Web Manager (https://groups.google.com/forum/#!topic/ganeti-webmgr/84umQtMCXP8)