changed deleteVoxelCodeFromTree() to use recursion to allow for proper unwinding, updating of parent path
add markWithChangedTime() method as public method

Conflicts:
	libraries/voxels/src/VoxelNode.cpp
	libraries/voxels/src/VoxelNode.h
fixed bug in recursive delete that caused animation ghosts
Made readCodeColorBufferToTree() use self contained recursion so we can
implement color averaging properly
added method for general subtree change bookkeeping
Merge pull request #495 from ZappoMan/recursive_voxel_delete

Fixes to delete voxel and color/add voxel to allow for unwinding color reaveraging