[TASK] Implement service to search for device updates

[Thaodan]

We have to implement a service that tells the Sailfish OS updater that there is a new update. For that we have to solve these underlying issues:

• How do we know that there is a new update for a device?
• Do we handle stop releases, how?
• Write the final service
• Document the process
• Configure the daemon

[Thaodan]

All done here.

Maybe mention how to set organization specific settings such as the repository from where to look for updates for later.