File permission/open state issue when upgrading the installer itself

When the updater itself is being updated (update, next, finished), after restarting the installer new content might appear. However, on this, second run, installing some of the packages fails with a "file blocked by another process" style error. If the restart of the whole QtCreator is mandatory, offer the user to restart QtCreator from the installer (not just restart the maintenance tool). Note: upon choosing "retry" the installer does continue.