Nerf fire cav (differently).

Give back their stacking fire, but reduce their damage, increase their spread and repeat time.
Based on the discussion at https://wildfiregames.com/forum/topic/72452-tasklist-for-closing-out-a26/, this should decrease their efficiency versus units.

Patch by: @marder
Differential revision: https://code.wildfiregames.com/D4516
Reverts r26474 / rP26474
Comments by: @Silier
Reviewed by: @chrstgtr, @ValihrAnt