[DO NOT MERGE] Calamity mode.

Putting this up for input/review, it's very rough at the moment and I can't work out how to easily squash it since the commits are distributed over a long timespan.

Calamity mode is a replacement for meteor. In a nutshell:
- For every X crewmembers, Y antagonists of Z type spawn.
- Random events fire much faster.

That's the mode in a nutshell.
Not directly related to calamity but, I'm a little ashamed of this despawn code I wrote. It really is a hack. Have you given any thought to replacing it or removing it?