cleaned up credit model (a bit), added scoped sessions for multi-threading
cleaned up credit model (a bit), added scoped sessions for multi-threading

Tristan79/ComicStreamer,davide-romanini/ComicStreamer,davide-romanini/ComicStreamer,beville/ComicStreamer,davide-romanini/ComicStreamer,mike-ferenduros/ComicStreamer,beville/ComicStreamer,Tristan79/ComicStreamer,Tristan79/ComicStreamer,Tristan79/ComicStreamer,mike-ferenduros/ComicStreamer,mike-ferenduros/ComicStreamer,mike-ferenduros/ComicStreamer,beville/ComicStreamer,beville/ComicStreamer,davide-romanini/ComicStreamer