A "Use High definition textures" option

Hello,
I added an option that can be disabled to use smaller textures.
A half-sized texture will be generated from the original HD texture and will be cached. And when the cached texture is older than the original version, the resized texture is regenerated.

Atm, half-sized textures are only used for tracks, but it can be extended to karts (and possibly other stuffs). Just tell me which other things should be affected by the option.

Haldric

PS: Are there any plan to reorganize the graphics settings dialog? / Have you already an accurate idea of the reorganization?