core: create qPrefFacebook from SettingsObjectWrapper

Update set/get functions to follow common name scheme:
- get function have same name as in struct diveComputer
- set function have set_<name>
- signal function have <name>_changed

one class one .h/.cpp is the C++ idiom. Having load/sync of each
variable in 1 functions (in contrast to the distributed way
SettingsObjectWrapper handles it) secures the same storage name
is used. Having the set/get/load/sync functions grouped together
makes it easier to get an overview.

REMARK: this commit only defines the class, it is not active in production

Signed-off-by: Jan Iversen <jani@apache.org>

core/settings/qPrefFacebook.h

@@ -0,0 +1,45 @@
+// SPDX-License-Identifier: GPL-2.0
+#ifndef QPREFSFACEBOOK_H
+#define QPREFSFACEBOOK_H
+#include "core/pref.h"
+
+#include <QObject>
+
+
+class qPrefFacebook : public QObject {
+	Q_OBJECT
+	Q_PROPERTY(QString access_token READ access_token WRITE set_access_token NOTIFY access_token_changed);
+	Q_PROPERTY(QString album_id READ album_id WRITE set_album_id NOTIFY album_id_changed);
+	Q_PROPERTY(QString user_id READ user_id WRITE set_user_id NOTIFY user_id_changed);
+
+public:
+	qPrefFacebook(QObject *parent = NULL);
+	static qPrefFacebook *instance();
+
+	// Load/Sync local settings (disk) and struct preference
+	void loadSync(bool doSync);
+	void inline load() {loadSync(false); }
+	void inline sync() {loadSync(true); }
+
+public:
+	static inline QString access_token() { return prefs.facebook.access_token; }
+	static inline QString album_id() { return prefs.facebook.album_id; }
+	static inline QString user_id() { return prefs.facebook.user_id; }
+
+public slots:
+	void set_access_token(const QString& value);
+	void set_album_id(const QString& value);
+	void set_user_id(const QString& value);
+
+signals:
+	void access_token_changed(const QString& value);
+	void album_id_changed(const QString& value);
+	void user_id_changed(const QString& value);
+
+private:
+	void disk_access_token(bool doSync);
+	void disk_album_id(bool doSync);
+	void disk_user_id(bool doSync);
+};
+
+#endif