Start working on FrameBufferObject backed pipe sign rendering

[davboecki]

This is an attempt to render the content of pipe signs into a frame buffer first before rendering it onto the sign. This way the content can be cached and hopefully, this will improve rendering of pipe signs significantly.

[2xsaiko]

Is there a reason for replacing GlStateManager methods with direct GL calls?

[davboecki]

Yes the framebuffer has his own state so using the MC state methods will mess things up. Well even like it is at the moment things are not working 100% correctly, it's still WIP.

[2xsaiko]

I'm pretty sure GL state is global and it won't change in any way when you bind a framebuffer. You even have to reset the matrix in most cases, since you want the stuff you're drawing to be drawn flat on the framebuffer texture, and not with the previous transformation applied.