Summary:
Users have complained that Kate's terminal doesn't use the same shortcut as Dolphin to
open and close. This patch makes it do so, using the same shortcuts that dolphin uses
to both open/close and also focus/de-focus:

F4: Open/close
Ctrl+Shift+F4: Focus/de-focus (also open if currently closed)

BUG: 414587
FIXED-IN: 20.04.0
Closes T12318

Test Plan:
Hit F4 twice -> terminal opens and closes
Hit Ctrl+Shift+F4 twice -> terminal focuses and de-focuses

Reviewers: #kate, cullmann

Reviewed By: #kate, cullmann

Subscribers: cullmann, kwrite-devel

Tags: #kate

Maniphest Tasks: T12318

Differential Revision: https://phabricator.kde.org/D25805