Refactoring: centralize GBDevice creation

- created and provided by DeviceHelper
- passed from UI to service
- without UI, service uses DeviceHelper directly

=> Cleaner and less duplicated code

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/model/DeviceService.java

@@ -3,6 +3,7 @@ package nodomain.freeyourgadget.gadgetbridge.model;
 import android.support.annotation.Nullable;
 
 import nodomain.freeyourgadget.gadgetbridge.devices.EventHandler;
+import nodomain.freeyourgadget.gadgetbridge.impl.GBDevice;
 import nodomain.freeyourgadget.gadgetbridge.service.DeviceCommunicationService;
 
 /**
@@ -60,6 +61,8 @@ public interface DeviceService extends EventHandler {
 
     void connect();
 
+    void connect(GBDevice device);
+
     void connect(@Nullable String deviceAddress);
 
     void connect(@Nullable String deviceAddress, boolean performPair);