Refine register/unregister function
Put custom properties together and removed some trailing spaces in import_pmx.py
Change _custom_props function to a dictionary
Merge branch 'powroupi-refine'
Merge commit '47b06ce86cc26bdd2872b1b93c3096cc7b1e68cc' into 0.5.0-dev

Conflicts:
	mmd_tools/__init__.py
	mmd_tools/import_pmx.py
Fix issues of ncc objects and bone track objects

- Some ncc objects might be missed in original for loop
- The ik constraints might change the position of pose bone in some case

Conflicts:
	mmd_tools/import_pmx.py
Some updates to import_pmd.py and import_pmx.py

Conflicts:
	mmd_tools/import_pmx.py
fix incorrect rotations of rigid body objects.

Conflicts:
	mmd_tools/import_pmx.py