Allow to register / verify a _support contract_ / device against our backend

[kelson42]

Once offspot/imager-service#533 implemented, we should have a way (on the admin UI) to deal with the registration.

At this stage, I see a simple entry requesting the support contract license number, which one give will be sent to the backend for registration.

Each feature depending of this registration, and its current validity, will need to verify it.