Support new model version API
Closes #185 (closed)
Based on teklia/arkindex/backend!1885
Use separted methods for creation and validation operations.
The publish_model_version
can be used as before (it should not break things).
I updated/wrote tests, but they did not cover the publish_model_version
.
I could add some, but they require to mock the unit method which is longer.
Edited by Valentin Rigal