Implement CFbsBitmap backend for QPixmap in OpenGL graphics system on Symbian

The default implementation of QPixmap in the OpenGL graphics system uses a QGLFrameBufferObject for storing data. This may not be optimal on Symbian due to the high graphics memory consumption of this type and the more constrained devices that we expect Symbian to be running on.

This task is about researching the different approaches (eg: CFbsBitmap, RSgImage etc.) and then making a decision based on required performance and memory usage constraints.