Tidied up collisions at wall interfaces.

Mostly fixed glitchy collisions when sliding along walls and passing
corners where rectangular and diagonal walls meet. Also added debug mode
(toggled with 'D') which currently draws an arrow for each collision
direction colour coded to show wall style (yellow: diagonal, red:
rectangular).
Merge remote-tracking branch 'origin/develop' into develop

Conflicts:
	Hunt.gmx/Hunt.project.gmx