Add support creating labels per API

##### What does this MR do?

As labels got their color feature, the API also needs some :heart:. This PR adds creating new labels via API.

##### Are there points in the code the reviewer needs to double check?

Creating a new label is refactored out to a service.

##### Why was this MR needed?

Currently, the API can only **get** labels

Surrounding space missing for operator '?'.