Async ending of gst pipeline in stream and media player sources caused a crash at termination as source was still not closed when process was ended. Fix is to ask for an immediate termination of gst pipeline upon delete of stream, and to wait for mixer manager to end current session when clearing.
StreamSource now have the option 'restart on deactivation' like MediaPlayer. This option is saved in XML (added Visitors for Stream and StreamSource). The GUI is added as sub-menu in play bar (like for MediaPlayer). Some StreamSource subclasses needed to be fixed to allow this feature (e.g. MultiFileSource).
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.