* Add "BuildSteps" table like in Hydra.
This will prevent package dependencies to be built multiple times.

* Add tests for the remote building mechanism.
- Write test cases covering the nominal remote building scenario, with a
  server dispatching build tasks to multiple local workers.
- Write test cases covering workers disconnection and reconnection.
- Write test cases covering build timeout.

* Improve the "/workers" page.
- Add build machines status (CPU, RAM) usage.
- The opensuse monitor page could be a good model:
  https://build.opensuse.org/monitor.

* Add new metrics.
- Add "build speed per machine" and "idle time per machine" metrics.

* Report build failures by email/RSS.

* Add a user account section.
- Add customized monitoring dashboards.
- Add build failures notifications subscription page.
- Add a substitutes availability service, so that users can be notified when
  the substitutes coverage of their manifest is passing a threshold.