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
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
SimulationEngine::enforceConstraints() takes args

...for limiting simulation costs
Changed RagDoll to Ragdoll
Ragdoll not an Entity.  SkeletonModel is a Ragdoll
Add shape vs list-of-shapes collision method

and list-of-shapes vs list-of-shapes
add way to enable Model for collisions
add API stubs to RagDoll for SimulationEngine stepForward
enable shape collisions for MyAvatar skeleton

also some stubbery for main simulation loop