First iteration of the port to KF5

Disables compilation of the plasmoid (C++ plasmoids are unsupported in KF5)
and the kcm because does crazy things with the QDeclarativeItems.
Tests don't pass but Alex promised he'll look at it.
Port of the KScreen KCM to KF5

It is quite verbose as it was using some intrinsic API of QGraphicsView that
is obviously not available anymore.
It seems to work to some extent now, but it would be really good if there
was some testing since I'm unsure about how to test it.

CCMAIL: Dan Vrátil <dan.vratil@gmail.com>
Fix compilation after KAboutData change
Fix problem when saving KScreen states

QJsonSerializer was not being called properly and it became useless.
Also make sure we're reacting properly to missing or unopened configuration
files.

Reviewed by Alex Fiestas
Merge branch 'master' into frameworks
Use the correct kcmshell version (4 → 5).
i18n fixes
-Wmissing-include-dirs
--warning
Adjust weight in systemsettings
iconSizes has moved from theme to units
Merge branch 'master' into frameworks

Conflicts:
	kcm/qml/main.qml
	kcm/src/kcm_kscreen.cpp
	kcm/src/outputconfig.cpp
	kcm/src/outputconfig.h
	kcm/src/widget.cpp
Make Output Identifiers work again and improve it a little
port to QWidget::createWindowContainer

unfortunately QQuickItem is not reliable enough for 5.1

Note that the outputIdentifiers should always be QQuickView
regardless, as they are top level windows