Add isUsed bindings to pySimpleStateVariable

This lets python scripts determine if variables in SDL blobs are used (at
the default).
Refactor avatar movement code

plMovementStrategy classes have been reworked and completely replace all plAvatarControllers.
While based on the old implementation, plPhysicalControllerCore has essentially been rewritten.
Remnants of long gone physical "actions" have been removed.

4 files removed -
plAVCallbackAction.h & plAVCallbackAction.cpp
plAntiGravAction.h & plAntiGravAction.cpp

This revision will not compile, requires new plPXPhysicalControllerCore implementation.
Updated plPXPhysicalControllerCore

While based heavily on the old implementation, this is essentially a rewrite.

Notable changes -
Controllers are now updated at the same fixed frequency as the simulation.
Resulting output is interpolated between steps to precisely match the frame delta.
Physics work is only done when enough time has passed to perform a step.

The kinematic actor that followed around the controller has been removed.
The underlying kinematic actor created by the NxController is now used for triggering.
A new sim group was added for a kinematically controlled avatar.

2 unused files removed -
plPXPhysicalController.h & plPXPhysicalController.cpp
Remove some PhysX workarounds that are no longer required.
Fix horizontal mouse-look while standing still.
Improve simulation timing at low frame rates.

Increased kDefaultMaxDelta to 0.15.
Added a small bias to combat a truncation issue.
Fix subworld transition bug

Use the actual global location, not the interpolated location when moving between subworlds. Rebuild the controller cache.
Fix warping an avatar triggers all detectors along the path

When explicitly moving an avatar over the given threshold, teleport the underlying actor most of the way before moving the controller.
Fix controlled flight bug

fControlledFlight state should be handled outside of the physics step.
Disabled avatar updates

Only update disabled avatars between steps if in a subworld and then don't
interpolate their position.
Clear linear velocity after each update.
Clear impact velocity on WalkingStrategy Reset.

Fixes landing behaviours incorrectly firing after a brain transition.
Clear achieved linear velocity on disabled avatars.
Only apply height correction to human avatars.
Rework PhysX collision flutter bug workaround

To better handle erroneous trigger events under the new timing method, use the number of times the simulation has actually advanced instead of the number of evals received.

Cleaned up a bit.
Include a comment that explains the humanness check

Following a suggestion from @branan, I've added a comment that points out
that the controller makes a different sized kinematic actor if the
armature is human (male or female)
Merge pull request #234 from Hoikas/sdl-isused

pySimpleStateVariable IsUsed Binding
Merge pull request #230 from Hoikas/physx

PhysX Cleanup (forward port from OU)
Fix Cloth Links

A typo introduced in 49dfb4e5 caused camera stacks in AgeLink nodes to
overwrite spawn point names. This broke shell and journey cloth links in
the Relto bookshelf.
Fix crash in PtGetCameraNumber()