Update calls to steering API to handle HTTP status codes

Currently HTTP Status codes in the responses from the Steering API cannot be handled by the dashboard.

We should update the calls to the steering API to handle them consistently:

• a request to create an object already returns a 201 (Created) status,
• a request to update an object already returns a 200 (OK) status,
• a request to delete an object already returns a 204 (No Content) status,
• a request with missing or wrong parameters already returns a 400 (Bad Request) status,
• a request to create a schedule will return a 201 (Created) status if the operation doesn't result in collisions in the timeslot or they can be solved with solutions offered,
• a request to create or update a schedule will return a 409 (Conflict) status if the operation results in collisions in the timeslots that need to be resolved.