[Linux] Implement proper disconnection detection (#95)

* [Linux] Implement proper disconection detection

* Only trigger on airpod devices

* Remove unused code

* [Linux] Fix SegmentedControl text not shown in release build (but debug builds showed text)???

linux/BluetoothMonitor.h

@@ -0,0 +1,26 @@
+#ifndef BLUETOOTHMONITOR_H
+#define BLUETOOTHMONITOR_H
+
+#include <QObject>
+#include <QtDBus/QtDBus>
+
+class BluetoothMonitor : public QObject, protected QDBusContext
+{
+    Q_OBJECT
+public:
+    explicit BluetoothMonitor(QObject *parent = nullptr);
+    ~BluetoothMonitor();
+
+signals:
+    void deviceConnected(const QString &macAddress);
+    void deviceDisconnected(const QString &macAddress);
+
+private slots:
+    void onPropertiesChanged(const QString &interface, const QVariantMap &changedProps, const QStringList &invalidatedProps);
+
+private:
+    QDBusConnection m_dbus;
+    void registerDBusService();
+};
+
+#endif // BLUETOOTHMONITOR_H