Re-Enable --hide-tabbar and --show-tabbar

Summary:
Show tabbar and hide tabbar got lost in the transition to a modern
QTabBar, this re-enables them. These options will override the
current settings if you use --hide-tabbar or --show-tabbar.
Changing these options in the settings will change these settings.

To use the current preferences just start konsole without --hide-tabbar
or --show-tabbar

Reviewers: Konsole, sandsmark, hindenburg

Reviewed By: Konsole, hindenburg

Subscribers: ngraham, konsole-devel

Tags: Konsole

Differential Revision: https://phabricator.kde.org/D14294