Fixed#3660. Removed using of GUI class in Profile Importer. Because, it
cannot be used before Nexus instance will be created. As result, it
provide crash in some cases.
Importing a profile, saving a QR code image or setting an auto-accept directory using Nautilus as the default file manager, which many users use, was causing a hang in Qt's method. Setting Qt to use it's own file manager in this circumstance fixes the issue. Closes#3436, closes#3443.