- make ortho grid drawing use vertex arrays
- make perspective view floor drawing cache result of UI_ThemeColorShade so its not called on every line.
- make perspective view floor only loop once on each axis when the grid floor isnt being drawn (was looking over all grid lines for no reason).
- add UI_GetColorPtrShade3ubv() to replace UI_GetColorPtrBlendShade3ubv() when no blending is needed.