Prevent duplicate focus execution.

This MR quickly fixes the possibility to start the focus procedure twice or more at the same time, by checking the inAutoFocus flag before running. It also relocates startup checks before causing side effects, enforcing prerequisites before anything else.

It comes with a test validating the behaviour.

Note that other d-bus calls are able to cause side-effects with no regards for a possibly running procedure, so more tests and fixes are required.