Summary:
This change introduces an OrientationSensor class which wraps a
QOrientationSensor. The OrientationSensor is hold by Screens and gets
enabled if Screens knows about an internal (e.g. LVDS) display which
supports rotation. In addition the OrientationSensor holds an KSni to
enable/disable the automatic rotation support.

The drm platform plugin is adjusted to make use of the OrientationSensor.
The API is defined in a way that this can also be implemented on other
platforms supporting rotation. Most important are hwcomposer and X11
standalone. The latter should be straight forward as rotation is provided
through XRandR. The former needs addition for rotation support first.

Test Plan: Rotated my Yoga 12

Reviewers: #kwin, #plasma, sebas

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D8699