Ask for confirmation when Closing Dolphin windows with a terminal panel running a program

Summary:
Ask for confirmation when Closing Dolphin windows with a terminal panel running a program.

FEATURE: 304816
FIXED-IN: 19.04.0

Test Plan:

1. Open terminal panel
2. Run watch ls
3. Close Dolphin
4. Observe confirmation
5. Disable confirmation
6. Repeat, observe no confirmation
7. Enable confirmation in the settings
8. Repeat, observe a confirmation

Reviewers: Dolphin, markg, elvisangelaccio, rominf

Reviewed By: Dolphin, elvisangelaccio

Subscribers: kfm-devel, elvisangelaccio, markg, ngraham, rkflx, broulik, Dolphin

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D10960