[sch/brd] 'Esc' should unwind trace/wire placement when laying traces/wires

[abetusk]

When hitting 'Esc', the whole action gets cancelled. It would be nice to be able to hit 'Esc' and go back incrementally instead of discarding the whole trace placement. Maybe hitting something like 'q' could do a 'hard' quit.

priority:medium estimate:5