Add InitMaterial2D member, which will be used to alter 2d render state settings. Not yet functional, though, as we need to do more performance tests and API additions.
Added the 2d batch render function to OpenGL as it reduces the amount of render state changes. This makes text rendering far better scaling.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@3023 dfc29bdd-3216-0410-991c-e03cc46cb475