Add cg_fovMin support

[HalfOfAKebab]

cg_fovMin controls the minimum field of view, which is most obviously used when aiming down sight. I like to have cg_fovMin equal to cg_fov, so when I aim down sight there is no zoom effect. Some other people might like to increase the number slightly so the ADS zoom isn't so jarring when playing at higher FOVs.