The integration, screen, window and cursor classes were split in Qt 5.3 under a plan
of sharing these between eglfs, the Android port and potentially other future plugins.
This never materialized.

Maintaining the artificial split is getting difficult and is prone to errors. Therefore
it is time to merge back these base classes into eglfs. The result is cleaner, smaller,
and potentially better performing code. eglconvenience is now restored to be a collection
of convenience classes instead of platform plugin bits.

Change-Id: I75c6ad876ef66a1a0c5b39c1c307f928d2ed47d4
Reviewed-by: Louai Al-Khanji <louai.al-khanji@theqtcompany.com>