Config.delete_profile does not write changes to file

[sphuber]

This means that the profile is not removed from the config.json. The method should call self.store() before returning and we should add a test. Tricky part is that in the test we cannot use the Config method to check if the profile still exists, because it won't in memory but we need to check that the file on disk is properly updated as well.

It should also check if the deleted profile was the default, and if so reset it.