Introduce a QCommandLineParser for kglobalaccel5
Summary: It's useful to be able to check the version and so.
Test Plan: Running kglobalaccel5 --help doesn't execute the service.
Reviewers: Frameworks, davidedmundson
Reviewed By: davidedmundson
Subscribers: graesslin
Tags: Frameworks
Differential Revision: https://phabricator.kde.org/D4175