GPII-716: PCP's method for interaction with FM via WebSockets should be more declarative

Link to JIRA: http://issues.gpii.net/browse/GPII-716

This pull request is strictly connected with Websockets communication from PCP to FM (http://issues.gpii.net/browse/GPII-539) and is not related to the pilots.

The changes this pull request brings are:
 - "Save" button in PCP applies the changed settings directly to the system by using websockets. It doesn't use the logout+login mechanism (to eliminate the chance of unexpected issues),
 - "Save" doesn't save to the prefs server.

Once this pull request is in, there will be three more (short ones) for:
 - Making this change happen instantly after a change in the model, rather than by pressing Save,
 - Making the save button save to prefs server,
 - Making the "full editor" link forfeit the logout+login mechanism as well and start functioning as the save button + switching to PMT.
@jobara Connecting the socket is most often done only once, but disconnections might happen (socket receiving 'disconnect' event) during the lifetime of the socket for different reasons. The socketConnected flag is used to ensure that the socket is connected each time we try to emit a message.