Add range overlay to artillery.

Structures have them since r20608 / rP20608, but units were excluded there due to their mobility and amounts.
Artillery is not that easily massed and also not very mobile, but has a high range and damage with a low reload time, making it nice to know their approximate range.

Patch by: @Nescio
Differential revision: D3606
Comments by: @Angen, @borg-, @wraitii