cleanup of avatar collisions, prep for more ragdoll collisions

removal of paddle hands
particles use general sphere collision path against avatars
temp removal of skeleton self collision
cleaup: remove some unused collision code

remove CollisionInfo::_type
remove unused Avatar collision response stuff
comment out some code that works but will probably be replaced
move RagDoll to libraries/shared
fix some comments
Use NULL Shape* for non-colliding joints in Models
clearShapes(), rebuildShapes() need not be virtual
RagDoll keeps a pointer to list of shapes
Add simulationID to Model Shape and CollisionInfo
merge
merge upstream/master into andrew/ragdoll
added _missingSequenceNumbers tracking to OctreeInboundPacketProcessor
added code for AC to send nack packets; no locking yet
added locking on _singleSenderStats; untested!
add PhysicalEntity class

Model and RagDoll derive from PhysicalEntity
Shape gets back pointer to its Entity (shape sharing not possible)
CollisionInfo gets backpointers the shapes involved
add SimulationEngine, MyAvatar has one.
Only build shapes for models that need them
Revert "added locking on _singleSenderStats; untested!"

This reverts commit c542da97076ba0d27f4e191ae5d8249dbf8afe7e.
Revert "added code for AC to send nack packets; no locking yet"

This reverts commit 15bd0878c407ede95f724009adadc81deeb7b4fd.
rollovers are now handled in SingleSenderStats::trackInboundPacket
SimulationEngine::enforceConstraints() takes args

...for limiting simulation costs