Changed climbing to one-handed dominance

[Malcolmnixon]

This pull request implements feature #210 by making climbing use a single dominant hand.

[BastiaanOlij]

Brilliant, I'd have to play with it a bit in game, I'm wondering how well things work if you grab with your left hand, now grab with your right, pull yourself up with your right and then let go with your right.

The dominant hand now changes back to your left hand, but it is now no-where near where you originally grabbed the wall. It may look weird if you continue to climb with your left hand when its new starting location is somewhere floating in space...

Or do we ungrab the left hand in this case when it moves off far enough?

[Malcolmnixon]

If the secondary hand moves more than 1 meter from its grab-point (either because the primary hand has moved the player, or the player moves their secondary hand) then the secondary hand grab is released. If the player then releases their primary hand then the player will fall.