Added damage-based regen, and support for AFK.

* Added soap_dmg_heal_ratio. If you set it to 0.5, and you do 100 damage to someone that dies within the next 10 seconds, you will get a 50 hp boost.
* Added support for a not yet released AFK plugin. Whenever someone is AFK, they will be teleported to the spawn room. When they return, they are teleported back into the battlefield.