Improve 3D components section in item library

Having all 3D related modules imported results in a bit messy Item Library when Quick3D, Quick3D Effects, and Quick3D Materials are presented in their own sections and each of them have their own subsection to custom shader utils, see attached picture.

Suggestions for improvement:

• One main section to all 3D modules that contains subsections for
  • Qt Quick 3D 
  • Qt Quick 3D Materials
  • Qt Quick 3D Effects
  • Qt Quick 3D Custom Shader Utils
• Instead of separately importing quick3d, quick3d materials and quick3d effects -> only one import needed to get them all
• Allow user to remove subsections that are not needed
• Imported 3D components should go under common section, e.g. "My Quick3D Components" instead of their own sections, see attached picture.