SpawnState

Depends on #450 

This is important for Scripting but can be packed into an isolated PR, I think that's prefered by everyone.

WorldObjects do have a spawnstate now indicating whether they are spawned, scheduled, rejected and so on. It replaces the old scheduledForRemoval() query.

Important for scripting is the possibility to disable deletion of rejected objects. scripts can try to spawn objects at another point, for example.