Fixes the 'drone' sprite for borgs.  The eyes are now actual eye sprites instead of attached to the base sprite.  No more pumping 40 shots into a secborg and wondering why it won't die.
Adds option for medical module to use the medical drone sprite.
Adds sprite for surgery and mining.  Mining will no longer use a medical sprite (why???)
Merge pull request #7172 from Neerti/11_29_14_minor_borg_drone_changes

Minor changes to drone borg sprite.