Use DECSCUSR 0 to reset to default

Summary:
This isn't standardized, but matches what VTE does.

printf '\e[0 q'         # reset to default

Ref. https://bugzilla.gnome.org/show_bug.cgi?id=720821 and
https://bug720821.bugzilla-attachments.gnome.org/attachment.cgi?id=291238

Reviewers: #konsole, hindenburg

Reviewed By: #konsole, hindenburg

Subscribers: hindenburg, ahmadsamir, konsole-devel, #konsole

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D17266