Blender Git Loki

Minor bug-fixes and optimizations.

* Change most instances of division and modulo with TILE_SIZE to bit shifting. Much more efficient since TILE_SIZE should be a
power of 2.
* Added intialization for some Mesh members. Previously had motion blur randomly toggle on and off otherwise.
* Fixed issue where voxel to tile correspondence is different between external VDBs and internal sparse grids. The fix requires
generating a new VDB grid which may be too memory intensive. Better method would be translating grids in place.
* Fixed misc OpenVDB to grid conversion issues.