Things are registered with duplicated KNoT IDs

After registering devices on the gateway web interface just notice that some of them were created with duplicated IDs. It seems there is a lack of checking before the registration process. Moreover, when one of these duplicated things is unregistered, the other ones can't be accessed anymore, maybe because the `uuid-alias-service-lookup` can't resolve the `id` anymore since only one `id` alias is registered on `uuid-alias-service`.

Result:
[devices.txt](https://github.com/CESARBR/knot-cloud-protocol-adapter-websocket/files/3535763/devices.txt)