updated bullet to 2.81-rev2613, in hope of fixing the btQuadword crash

Signed-off-by: Miles Whiticker <miles.whiticker@gmail.com>
temp fix for the btquadword crash, seems to be working so far

Signed-off-by: Miles Whiticker <miles.whiticker@gmail.com>
jumping works irregardless of gravity direction, mobs/atoms will now properly update about their cell position, gravity handles much nicer (not happy with how mob orientation is reset), gravity changes propogate downwards from the gravity plate to the cell contents, cells properly monitor their contents now and atoms can fire off events to other atoms in the same cell, mob control (looking & walking) is now nicer and works properly irregardless of gravity direction

Signed-off-by: Miles Whiticker <miles.whiticker@gmail.com>
fixed a longstanding bug (see blog post) in cell positioning

Signed-off-by: Miles Whiticker <miles.whiticker@gmail.com>
tweak to client camera resetting, mobs and objects now collide with each other

Signed-off-by: Miles Whiticker <miles.whiticker@gmail.com>