removed: BackGroundInfo Loader multithreading (no longer needed)
changed: Split background info loading into a 2 stages

This allows us to first perform loading of fast stuff and after that load the slow stuff (partially fixes #14071)
changed: Renamed m_database to m_videoDatabase and m_musicDatabase for clarity
changed: Use a member variable for the texture database to speedup thumb loading
changed: Factor out itemDone argument for Stage1
changed: Have the texture db member in the base class