Removed PLSM2 scene manager.

As the Terrain Component now handles terrain.
Don't reference deleted value.

Some compilers can alter the value after it's deleted.
Delete pages when removing bridge.
Extend time logging.
Make the compile methods const.

Since these are called in the main thread once all data has been set up
we'll make it clearer that they are supposted to not alter anything.
Fixed thread-unsafe code.

We can't access Terrain and TerrainGroup data in a background thread.
Add option to disable auto movement mode.

This is the feature where we automatically switch to movement mode when
entering the world.
Handle terrain material errors.

Make sure that if there's an error, that's not propagated up, or to the
terrain component.