Move mimetype-handling functions to own file (mimetypes.cpp). In MainWindow::openArchive() set filter using QFileDialog::setMimeTypeFilters() instead of using QFileDialog::setNameFilters().
This fixes sorting of filters in "Open Archive" dialog with KF 5.20.0. Frameworkintegration 5.20.0 broke this sorting due to commit 415ad2ed48356c3065c937813888fa1bd2742789.