Allow saving/restoring layout of key list to/from custom config group
- Make KConfigGroup argument mandatory (to prevent wrong usage).
- Add config group argument to saveLayout() and restoreLayout() and make both methods public.
- Automatically save/restore layout only if config group was passed to constructor.
- Explicitly, save/restore layout of key list(s) to/from custom config groups. Previously, the layout was saved to/restored from the config group "KeyTreeView_default" implicitly.
- Explicitly, use config group "KeyTreeView_default" for temporary key lists (e.g. after importing certificates). Previously, this config group was used implicitly.
- GnuPG-bug-id: T5175