This gets us one step closer to a public QSGTextureProvider
API.

This patch also includes a fix to the material ownership in
QSGCustomParticle.

Change-Id: I620e3006816db0c37eedf3a20a0d4cbe7a783b82
Reviewed-on: http://codereview.qt.nokia.com/3317


Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Kim M. Kalland <kim.kalland@nokia.com>