add head action server

from #41 (Repair from master branch to development)
It is a very interesting idea using this same 'parameters' mechanism from Grippers across other classes to manage their python class settings.  However, it seems at the moment this new parameter and the new code in this file is not used anywhere in this file / this class itself by any other functions in here - you just appear to be accessing it from the action server code. I think it might be better to move this new code to the head action server class for now (rather than here in the head class).