Merge pull request #589 from machinelevel/dev

(re-commit) Added support for Leap finger-sensing device.
fix the default orientation for an injector
Merge pull request #590 from birarda/voxel-noise

fix the default quaternion for audio injectors
Merge pull request #591 from machinelevel/dev

Update .gitignore to exclude the Leap SDK files, but not the stub header
Hand rework in preparation for adding send/receive hand data
- Added Hand.cpp, Hand.h, HandData.cpp, HandData.h, roughly matching the equivalent Head files
- Cleaned up Avatar by moving hand work into Hand files
- Added fixed-point data packing, for use in sending hand offsets