Fix content library visibility logic when there is no material library or QtQuick3d import

Materials tab should be empty and show some kind of informative message when there is no material library of QtQuick3D import.

Textures/Environment tabs should always be available, as image import is always valid.

Disable "Add Texture" and "Add Light Probe" menu options when there is no QtQuick3D import. "Add Image" is still valid option even with no quick3d import or there is no material library node.