The porting to Qt5 broke the timestamp handling in many areas. A deeper
look into Qt's xcb plugin shows that the appTime handling is not
sufficient for KWin's need. E.g. the time is only updated in response to
a property notify event if it's for a Qt created window, which is hardly
ever the case in KWin. Another example is that key press/release events
never updated the appTime.

As the functionality in Qt is rather trivial we can do the timestamp
handling ourselves. We filter all events anyway and it is slightly faster
as we don't have to go through the QPA interface any more.

REVIEW: 122636