Added basic ray intersection testing to VoxelTree.
Remaining pick bits.
Pointers to references for in/out parameters, renamed line parameter to more
descriptive "distance."
Missed a spot with the conversion from pointers to references.
Merge branch 'master' of https://github.com/worklist/hifi

Conflicts:
	libraries/voxels/src/VoxelTree.h
Merge pull request #198 from ey6es/master

Support for generating pick rays and finding intersections between rays and voxel nodes.