Summary:
This change allows users to scroll through krunner output using their homerow.

 - Ctrl+j: Scroll Down
 - Ctrl+k: Scroll Up

This makes scrolling easier for those familiar with this convention but doesn't inhibit users who aren't.

Reviewers: broulik, #plasma_workspaces, davidedmundson

Reviewed By: #plasma_workspaces, davidedmundson

Subscribers: davidedmundson, #plasma_workspaces, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D13686