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.cpp

@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "qPref.h"
+#include "qPrefPrivate.h"
+
+static const QString group = QStringLiteral("WebApps/Facebook");
+
+qPrefFacebook::qPrefFacebook(QObject *parent) : QObject(parent)
+{
+}
+qPrefFacebook*qPrefFacebook::instance()
+{
+	static qPrefFacebook *self = new qPrefFacebook;
+	return self;
+}
+
+void qPrefFacebook::loadSync(bool doSync)
+{
+	// Empty, because FB probs are not loaded/synced to disk
+}
+
+void qPrefFacebook::set_access_token(const QString &value)
+{
+	if (value != prefs.facebook.access_token) {
+		qPrefPrivate::instance()->copy_txt(&prefs.facebook.access_token, value);
+		emit access_token_changed(value);
+	}
+}
+
+void qPrefFacebook::set_album_id(const QString &value)
+{
+	if (value != prefs.facebook.album_id) {
+		qPrefPrivate::instance()->copy_txt(&prefs.facebook.album_id, value);
+		emit album_id_changed(value);
+	}
+}
+
+void qPrefFacebook::set_user_id(const QString &value)
+{
+	if (value != prefs.facebook.user_id) {
+		qPrefPrivate::instance()->copy_txt(&prefs.facebook.user_id, value);
+		emit access_token_changed(value);
+	}
+}