Until now we only used the XRandR events to know that a change happened,
then we went and queries X server for all the data to update our internal
cache.

This patch changes the behaviour so that we actually take all the
information available in the change event, and apply them to our cache,
so that we don't have to perform X-calls to get information we already
have.

To make full use of the events, XRandRCrtc class is introduced. An XRandrCRTC
object represents a single CRTC available on current machine. XRandRCrtc
objects are either "disconnected", or are linked to a specific XRandROutput,
to which they provide relevant information. Information availabe in
RRCrtcChangeNotify  and RROutputChangeNotify events are then used to keep
those up to date.

Since we already have up-to-date CRTC information now, we can also get rid
of the endless querying for free CRTCs when applying changes.

All in all, this seems to improve the speed in which we are able to react
to changes and reduces the X stutter caused by excessive queries to X. There
is still problem in QXcbConnection which handles XCBRandR events in a rather
ineffective way, causing huge delays and load on X, but that has to be fixed
in Qt.