Make sure the Image texture provider does not return an atlassed texture

Make sure the Image texture provider does not return an atlassed texture

This has the implication that textures from texture providers are always
the complete texture with coordinates from 0-1, which is means we get
a copy for atlas textures which may end up affecting performance.

Alternatives are:
 - ShaderEffect does this, which means texture providers can provide
   atlas textures.
 - We expose the subrect to ShaderEffect, which means an API
   change in all shader effect classes, and let the vertex shader
   solve this. Worst API, fastest and most memory efficient.

Change-Id: Id58eb866f315012637345a6f731626abf4a7a86c
Reviewed-on: http://codereview.qt-project.org/6029
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Kim M. Kalland <kim.kalland@nokia.com>