[OJElectronics] Add SignalR for requesting data from OJ Electronics cloud (#13782)

* Fixed some Nullable annotation warnings
* Use SignalR instead pooling

Signed-off-by: Christian Kittel <ckittel@gmx.de>

bundles/org.openhab.binding.ojelectronics/NOTICE

@@ -11,3 +11,8 @@ https://www.eclipse.org/legal/epl-2.0/.
 == Source Code
 
 https://github.com/openhab/openhab-addons
+
+Signalr4j
+* License: Apache 2.0 License
+* Project: https://github.com/sputnikdev/bluetooth-gatt-parser
+* Source:  https://github.com/sputnikdev/bluetooth-gatt-parser