Antialiased off-screen rendering in GLGraphics

Thanks to the contribution of Ilias Bergstrom, GLGraphics now allows to create off-screen drawing surfaces with 4x (and even higher) antialiasing!

GLTexture renamed to GLGraphics.

The GLTexture library mentioned in earlier posts got renamed to GLGraphics in this new release, since it incorporates some new functionality that goes beyond the original scope of the GLTexture class. It introduces a new renderer called GLGRAPHICS that descends from the built-in OPENGL renderer. However, GLGRAPHICS can be created without attaching it to any drawing surface, so it can be used as an off-screen render framebuffer.