Merge sensor changes

These changes will require a database update and will require app/website to handle the new sensors.

@jakobmoellers, @dwilhelm89 will there be any problems if we push the changes from #47 to dev/master? I'll replace the existing testsensors with new dummy sensors, but the names will become ObjectIds and any hardcoded sensors in the app have to be changed…

* [sensor.json](https://github.com/car-io/car.io-server/blob/sensor/rest/src/main/resources/schema/sensor.json)
* [sensor.create.json](https://github.com/car-io/car.io-server/blob/sensor/rest/src/main/resources/schema/sensor.create.json)