Investigate possibility of generating texture files in multithreaded way in 3D import

When importing 3D assets with a lot of baked in textures, QImage::save takes significant amount of time. E.g. importing asset with 40MB of textures takes over 10s compressing the pngs. If this process could be multithreaded (e.g. doing each save on separate thread), significant speedup could be realized for cases where there are multiple different textures.

If this seems feasible, separate implementation task can be created or the implementation can be done in context of this task as well.