Added 99% functional weaponmodel bobbing code. It even tries to stop bobbing when...

Added 99% functional weaponmodel bobbing code. It even tries to stop bobbing when you're not on the ground, and smoothly transitions between bobbing and not bobbing. The only problem is it seems to jolt whenever you pass through a message trigger or pick up an item or do anything unexceptional like that. Was it a bad idea to trust cl.onground?

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@5653 d7cf8633-e32d-0410-b094-e92efae38249