Select application after it is added

Summary:
After adding an application, an user will probably want to edit shortcuts for
the new application. Having to select it again is cumbersome.
BUG: 421331

Test Plan: Add an application.

Reviewers: broulik, ngraham, Plasma, mart

Reviewed By: Plasma, mart

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D29644