Master Shutdown

This commit adds the possibility to send the master to the background. The websocket and HTTP server will then be shut down, informing connected remotes to disconnect. Furthermore, the web library will disconnect.

Unfortunately, there is still quite a number of problems with this release:
- The master does not properly resume the webserver yet
- It seems UIWebView are bugged when it comes to websockets: sometimes when opening or closing a websocket, WebThread will crash randomly. We avoided this when shutting down the server by not closing the websockets but instead just telling connected remotes to fake-disconnect. This problem still persists when connecting to a remote, though.