Added GrindsUnit trait for RA2:YR-style Grinder structure logic.

Added GrindsUnits trait:
	int RefundPercent
	bool RefundPassengers
	string GrindSound

Code style cleanup in Passenger.cs

Added bool DrawPips to SelectionDecorations.cs
	Need a way to show normal cursors (non-cargo)
	even if we have `Cargo:`

Test case in RA with POWR (will remove after testing):
	Accepts inf and vehicles (APCs),
	note: does not play nicely with EjectOnDeath