[WIP]: Implement PolkitQt1 Authorization backend

Summary:
It is PoC patch which implements an Authorisation back end for ExternalCommand. It is still in progress.
Depends upon D21773

Test Plan: Compiles

Reviewers: stikonas, cjlcarvalho

Subscribers: KDE Partition Manager

Tags: KDE Partition Manager

Differential Revision: https://phabricator.kde.org/D21970