Qt Quick high-dpi support.

Set the device and viewport rect to the full device
pixel size. Set the projection matrix to the device
independent pixel size.

Scale shader effect source texture sizes.

Change-Id: I61dd546ff36a7ce6ad05f908796555674c714c1a
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Jens Bache-Wiig <jens.bache-wiig@digia.com>
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>