Add a new static lib and module for OpenGL extensions

The complete set of OpenGL extensions is large meaning that any attempt
to incorporate them into a shared library such as QtGui would bloat the
size of that library.

The typical usage pattern for OpenGL extensions is to use only a very
small number of extensions from the total available set. A static
library suits this situation very well as an application will only
compile in the executable code for the extensions actually used. Thus
makign all of the functionality available to those that need it but with
zero cost to those that do not.

Change-Id: I49fdac7e9d2e0b190b7ea04b776018dd63c3065f
Reviewed-by: Samuel Rødal <samuel.rodal@digia.com>