Do screen filtering by screen geometry rather than number.
Summary:
Avoids problems stemming from libtaskmanager and plasma-framework's
AppletInterface::screen numbering screens differently (QScreen order
vs. who knows what).
CCBUG:365246
Reviewers: Plasma, graesslin, mart
Subscribers: plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D2143