Doors, Lifts, other mutable geometry

[jmickle66666666]

My plan for this is to do a pre-pass on the level before triangulation. Any moving sector will be tagged and excluded from the initial mesh generation. It'll still need to get triangulated later on.

The non-moving parts of the sectors will still need generating.

They should list the minimum and maximum positions, and when building the mesh they need to be set to the most "open" they can be: lifts at the floor, doors at the top, crushers at the top etc.

Then after the map is built, new objects will be created for those sectors.