[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.
this too, if it's not specific to calamity and could be used by something else.