Modifies IMove & Enter and Fixes #4640 - Units teleport into transports

Adds more support for enter/exit/dock logic.
Fixes #4640 - Units teleport into transports.
IMO the way that the existing traits handle this (cancelling the activity from the inner order or removing the actor from the world if they don't want to exit) is a bit nicer than externally managing this state.  I'm not sure what your next planned steps are, but is this necessary?