rename QSGGeometry::stride() to sizeOfVertex for symetry with index

rename QSGGeometry::stride() to sizeOfVertex for symetry with index

Also support GL_UNSIGNED_INT as index type when supported by GL

Change-Id: I0988e102c8a04ce6cd02fb02528204ba810f853a
Reviewed-on: http://codereview.qt-project.org/4453
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>