Introduce concept of global and individual output data retention

Summary:
This is a new concept allowing the user to specifiy properties of a display
model (in best case identified by its EDID) on a global level.

This means independent of the setup/configuration of displays the display
model is part of its global properties are preserved.

The properties are for now:
* resolution,
* scale factor,
* rotation,
* refresh rate.

While redefining global values is possible at any time, user is also able to
specify for individual configurations special settings deviating from the
global values.

Test Plan: Manually. Autotest broken due to altered behavior.

Reviewers: #plasma, mart

Reviewed By: #plasma, mart

Subscribers: plasma-devel

Tags: #plasma

Maniphest Tasks: T10028

Differential Revision: https://phabricator.kde.org/D16991