Small skirmish update

Hi,

Ok, just a  few tweaks to skirmish, mostly internal stuff but I messed with object sizes a bit and fixed respawning so you respawn in a random spot after death - so no more lurking and spamming players with insta-death!

I also added 'B' key to toggle visualization of world's  'bounding volume hierarchy tree' on/off. This is for my own debugging but it's kind of cool if you're curious. The BVH tree is probably less than optimal right now, as earlier attempts at this suggest it's better to use different heuristics for static vs moving objects when building the tree, but it currently just treats everything as moving right now.