core: Split PlaybackManager up into smaller parts

The PlaybackManager was a giant class that handled UI bindings, fetching
stream URLS, playback logic.

It now has been split up into:

- ViewModel::PlaybackManager, which handles UI interfacing and allowing
  to swap out the Model::Playback implementation on the fly.
- Model::PlaybackManager, which is an interface for what a
  PlaybackManager must do, handling queues/playlists, and controlling a
  player.
- Model::LocalPlaybackManager, which is an Model::PlaybackManager
  implementation for playing back Jellyfin media within the application.
- Model::PlaybackReporter, which reports the current playback state to
  the Jellyfin server, for keeping track of played items.
- Model::Player, which handles playing back media from an URL and
  the usual play/pause et cetera.

In a future commit, this would allow for introducing a
Model::RemoteJellyfinPlaybackManager, to control other Jellyfin
instances.

core/include/JellyfinQt/model/playbackreporter.h

@@ -0,0 +1,58 @@
+/*
+ * Sailfin: a Jellyfin client written using Qt
+ * Copyright (C) 2021-2022 Chris Josten and the Sailfin Contributors.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ */
+#ifndef JELLYFIN_MODEL_PLAYBACKREPORTER_H
+#define JELLYFIN_MODEL_PLAYBACKREPORTER_H
+
+#include <QLoggingCategory>
+#include <QObject>
+#include <QScopedPointer>
+
+namespace Jellyfin {
+
+class ApiClient;
+
+namespace Model {
+
+Q_DECLARE_LOGGING_CATEGORY(playbackReporter);
+
+class LocalPlaybackManager;
+
+class PlaybackReporterPrivate;
+/**
+ * @brief Reports the current playback state to the Jellyfin server
+ *
+ * Set a playbackManager using setPlaybackmanager() and this class
+ * will do its job.
+ */
+class PlaybackReporter : public QObject {
+    Q_OBJECT
+    Q_DECLARE_PRIVATE(PlaybackReporter);
+public:
+    explicit PlaybackReporter(QObject *parent = nullptr);
+
+    void setPlaybackManager(LocalPlaybackManager *playbackManager);
+private:
+    PlaybackReporterPrivate *d_ptr;
+};
+
+}
+}
+
+#endif //JELLYFIN_MODEL_PLAYBACKREPORTER_H
+