Fixed an issue that caused the 3 Death Knight units mods to be incompatible with each other.

Mod is now compatible with "Guv's Black Knight Hellsteeds"

Created new model for the Death Knights, and changed their mount to match their new appearance. Decided to put them on barded skeletal reaver horses, rather than the original blue Hexwraith mounts, which comes with a bit of a loss of speed, about 20 points lower, which has no significant effect on how they play. Unit cards have been updated to reflect the new appearance.

Updated the unit card to reflect the actual appearance of the units, rather than a lazy recolor of the hexwraith card.