Summary:
Assistant with two actions allowing you to either add a conventional macro-
based header guard or pragma-once.

Test Plan: Run `test_assistants testHeaderGuardAssistant`

Reviewers: #kdevelop, arrowd

Reviewed By: arrowd

Subscribers: apol, arrowd, kdevelop-devel

Tags: #kdevelop

Differential Revision: https://phabricator.kde.org/D17370