Fix monster spawn inside and in view of the player:

Added a dedicated function for spawning monster of a overmap monster group.

Allow spawning of monsters in plain view, this is needed upon game start or when moving vertically or upon teleportation.
Dirt floor for craters
Merge branch 'monster-spawn-inside-outside' of https://github.com/BevapDin/Cataclysm-DDA into merge