Add trailer evac

[kevinfoley]

In SWAT 3, after clearing a room and moving on, secured suspects and hostages would be invisibly evacuated by trailers and removed from the level. Add a similar feature.

[theengineertcr]

eez wanted to have a physical trailers, jose wanted to be able to carry hostages to the start of the level, resulting in them disappearing as you make it to exit. eez said he didnt want suspects and hostages going invisible after reports