More external force antags

[Rilor]

Well we currently have Wizard and nukies, And depending on your definition of external force, Blob, wraith, predator and the planned flockmind also count. There was a planned Martian antag and outsider which got scrapped because of bad critter code according to the wiki, I think Martian attempt 2 would be neat (because outsider seemed to just be flock but more ELDRITCH). People say Flockmind is martian plus outsider, I see the outsider but not much Martian and based on the Wiki page martian should be unique enough to stand apart from wizard and nukies (assuming its done well)