add connector name to screen model

Summary:
to uniquely identify screens (in QScreen::name()) add the conenctor
name and id (such as HDMI-A-1) to the model identification

Test Plan: tested a full plasma session

Reviewers: Plasma, graesslin

Reviewed By: Plasma, graesslin

Subscribers: graesslin, plasma-devel, kwin

Tags: KWin

Differential Revision: https://phabricator.kde.org/D3341