Add a higher-quality grass preset

[Charon]

Currently, there are four grass quality presets: off, normal, distant, and ultra. But it's also possible to get higher quality grass by editing startup.cfg. I find no ill effects setting grass_distance to 600 (ultra is 300), although values above 800 or so seem to produce flickering under some conditions.

 

But manually editing this isn't ideal, because 1) any other changes to the graphics settings will cause this edit to be overwritten, and 2) it's not discoverable. Very few players know they can get better grass by editing this.

 

So: Add a Super-Ultra grass quality preset, with a value of 600.