Properly close search when hitting Escape

Summary:
When performing a search and the focus is no longer on the
searchbox, hitting escape would hide the searchbox but would
not really end the search.

Test Plan:
Search something in the terminal, then click within konsole
but outside the searchbox so that it loses focus and hit
escape. The search highlightings should now be removed.

Reviewers: Konsole, hindenburg

Reviewed By: Konsole, hindenburg

Subscribers: hindenburg, ngraham, konsole-devel

Tags: Konsole

Differential Revision: https://phabricator.kde.org/D16754

(cherry picked from commit 94676fbdb4a0204fbe426843c73fca5839e8f4b5)