Initial release for a rqt controller manager plugin

Allows users to unload/load/start/stop/view available controllers and view their name/state/type/hardware interface/resources.  No functionality yet exists for loading a controller from the parameter server or reloading libraries.

This is a preliminary release, I'm not sure if this works on other machines yet, but it seems to work smoothly on my own.  I'd like to see if interested parties would be like to test it and potentially prepare it for a hydro-devel merge.