Maintenance Drones

First stage implementation:

Has all things contained in Pete's old PR, Cleanup + RnD/Mechfab construction of them.

This stage is completely playable but lacks certain things. (If a Drone wants metal, it needs to go pickup some metal etc.) and little improvements will come with time.

No changes to maps as I suck at the Map merge tool and my Java hates my guts.
Suppose this leads it up to @Metacide or another mapper to design where to put some.
(I was thinking 2 in Robotics, 1 in Maint)

I don't *think* this needs a poll, the idea has had about 3 successful polls already, but if needs be go ahead.
also if this is the mob description it shouldnt say "shell" it should describe the actual drone