GCS Receiver API and GCS Control refactoring

This reopens @guilhermito's GCS Controller refactoring (https://github.com/TauLabs/TauLabs/pull/889).  This will restore HiTL functionality, which has been broken for several months now. I've added a patch which adds the pluginspec to the .pro file (solving the debug build issue) and explicitly removes the plugin from the manager when the plugin is destroyed.

Since this was previously reviewed and given the go ahead I'll merge this once jenkins is ready.