Add a "MMD Rig Tools" Panel.
Change the optimization method for constraints of "non collision groups"
Update README.md and CHANGELOG.md
Update README.md
Merge branch 'master' into exporting_pmx

Conflicts:
	mmd_tools/__init__.py
Add support for toon textures
Add support for importing sphere maps.
Add support for importing some properties of materials.
Add a "MMD Material Tool Panel".
Add support for sphere textures.
Change the "MMD Camera Rig".