This is an experimental spinoff from RigsOfRods#3049. I felt inspired.
Since the collision works by "sticking" the character to the actor while in contact, I realized I could extend our existing driver-attachment logic to also handle this attachment.��It's glitchy right now, partly because the networked cab offset is always in world coordinates, so it causes sliding when the vehicle turns.

Minor cleanup: removed the `enabled` param from `SetActorCoupling()` because it was dummy.

Bad outgoing data.

…king

how it works: once rorbot touches cab, it's position is 100% overriden by the cab position + rorbot's local position inside that cab's space (using transformation matrix).
currently cab collision is disabled, only the debug UI buttons can glue rorbot to cab.