Add possible border handling in minimize all script

Summary: Adds screen edge handling in minimize all script.

Test Plan:
With a hacked KCM, setting the option works perfectly and updates correctly
adding/removing the edge bindings as appropriate.

Reviewers: #plasma, graesslin

Reviewed By: #plasma, graesslin

Subscribers: graesslin, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D2263