* Re-add non-player sector damage.
Reimplements SECMF_HURTMONSTERS and SECMF_HARMINAIR.
* Fixed 3D floor handling for sector damage.
Fixes sector damage to either monsters or players not working on (non-)solid 3D floors.
- Added SECMF_HURTMONSTERS, which allows monsters in the flagged sector to be hurt with the same behavior as players (i.e damage leaking).
- Added SECMF_HARMINAIR, which allows players (And monsters with SECMF_HURTMONSTERS) to be hurt when they're inside the sector in general, instead of only when they're walking on it. Replicates the behavior of the DAMAGE_IN_AIR flag that SectorDamage() uses.
- Added NOSECTORDAMAGE, which makes actors with the flag immune to any harmful floors.