Preset file name of archive in CreateDialog

Summary:
The file name can be set explicitly by --add-to option or
detected automatically with --add option. Set it in the
dialog for the convenience of users.

Reviewers: Ark, elvisangelaccio

Reviewed By: Ark, elvisangelaccio

Subscribers: elvisangelaccio, kde-utils-devel, Ark

Tags: Ark

Differential Revision: https://phabricator.kde.org/D18152