- add TinyMutex to resolve the issue that we can not operate the virtools group infos of 2 individual objects.
* use this new class for all class need resource mutex, such as ballance element, bme materials and etc.
- add CollectionVisitor to resolve that blender have bad document and type hint for runtime bpy.types.CollectionProperty.
* now all visit to CollectionProperty are delegated by this class.
- add a new operator which can converte selected object to mesh, and if object is curve and has bevel object, it will copy the virtools group info of bevel object at the same time.
- add a hint in virtools group panel to tell user that the virtools group of non-mesh object will not be saved.