Performance improvements for 1.7 and 1.8

[naive carbon]

On windows and linux 1.7 is better for performance than 1.8 iirc.
On macos 1.8 has better performance than 1.7

1.7 uses openGL 1.2
1.8 uses openGL 2.1

So it would be useful if we could choose between openGL 1.2 and 2.1 on both minecraft 1.7 and 1.8

This is probably possible on 1.7 because openGL 1.2 code should run on 2.1 without any issues but idk if its possible to make 1.8 use openGL 1.2 (1.7 rendering) with its openGL 2.1 code.

[naive carbon]

(This would improve 1.7 performance on macos and 1.8 performance on windows and linux)