[Needs poll] [Needs testing] cult changes for lowpop

Cult minimum amount of players changed to 15.

Cult scaling changed:
15-19 ready players = 3 starting cultists.
20-29 ready players = 6 starting cultists.
30+ ready players = 9 starting cultists.

Convert rune now only requires 2 people for conversion. 2 is enough to enforce cooperation but no longer too difficult to organize if there are inexperienced players.