Replace assert with check and add exception.
Verify cacert existence before using it.

Closes #3362.
Merge remote-tracking branch 'ivan/bug/3362_check-if-cacert-exists' into develop
Fail gracefully when the events server fails to start
Merge remote-tracking branch 'chiiph/bug/fail_gracefully_events' into develop
Enable translation for string in code.
Update docstring and remove unused import.
Add cancel button to login. Closes #3318.
Add defer canceling to the app quit method.
Merge remote-tracking branch 'ivan/feature/3318_add-cancel-button-to-login' into develop
update comments
fix for none
reduce indentation
Properly shutdown soledad instance.