Some tweaks and refactoring to get rid of ContentLibraryMaterial in the
user section of the content library. The end goal is to unify the code
for handling all Qml components in the user section (materials, 3d
components, effects, 2D components. etc).
Change-Id: I99d4fb64dae0b52265994ce478525e574e4bc658
Reviewed-by: Ali Kianian <ali.kianian@qt.io>
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>