Marvin Mirtschin

Refactor static methods in singletons which change the state of the object to be non-static and be called via `getInstance()`.

``` 07-16 13:49:37.565 W/NearbyDevicesManager: Device scanning failed java.lang.ClassCastException: com.nexenio.authenticator.accesscontrol.GateEntranceDetectionBeacon cannot be cast to com.nexenio.authenticator.accesscontrol.GateDetectionBeacon at com.nexenio.authenticator.accesscontrol.GateDetection$1.onMatchingBeaconUpdated(GateDetection.java:93) at com.nexenio.bleindoorpositioning.ble.beacon.FilteredBeaconUpdateListener.onBeaconUpdated(FilteredBeaconUpdateListener.java:25) at com.nexenio.bleindoorpositioning.ble.beacon.BeaconManager.notifyBeaconUpdateListeners(BeaconManager.java:102) at com.nexenio.bleindoorpositioning.ble.beacon.BeaconManager.processAdvertisingPacket(BeaconManager.java:79) at com.nexenio.bleindoorpositioning.ble.beacon.BeaconManager.processAdvertisingData(BeaconManager.java:55) at com.nexenio.authenticator.networking.bluetooth.NearbyDevicesManager.onScanResult(NearbyDevicesManager.java:213) at com.nexenio.authenticator.networking.bluetooth.NearbyDevicesManager.lambda$startScanning$2(NearbyDevicesManager.java:147) at com.nexenio.authenticator.networking.bluetooth.-$$Lambda$NearbyDevicesManager$3z2AY2Ysie8a5mXIbx0mQPopEkY.accept(lambda)...