Sanitize Reinforcement Missions

Fixed Reinforcement Missions to function more sanely,
inside and outside of DRLA - We now build a list of
monsters that we should spawn, and take from that list
instead of hacking around it. We also now limit boss
spawns to 3 per map and rarify them so they will only
spawn with a 1 in 6 chance.
Bump the mission max difficulty a little

Bump the max difficulty +10% so we spawn 100% monsters
on Suicide mission difficulty.
Take that off of the TODO