Dolphin: Cleanup service settings page

Summary:
Just some little things :-)
- Refactor foreach
- Fix minor formatting issues
- Use auto keyword where appropiate

Test Plan: Compiles

Reviewers: #dolphin, ngraham, elvisangelaccio

Reviewed By: #dolphin, elvisangelaccio

Subscribers: elvisangelaccio, kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D29560