WTF did I think it would be a good idea to delete a source in a separate thread? This obviously causes a crash. To be investigated when a source tailes to delete... but should not happen...
All Stream report failure with logs, read in InfoVisitor for Sources. ImGuiVisitor for Sources also detect failure of source and its stream.
Cleanup of unused includes and functions.
When a source in a session fails, it is not anymore deleted after update; the Mixer keeps it in the session but detaches it from the scene. This way the user can access the failed source in the navigator (listed in RED), and Replace the source. The Replacement of source is available for any source. The source visitor does not skip a visit if the source failed.
