Add Zombie Dragon unit

[im-mortal]

• [x] Base tables and definitions

• [x] Unit Card

• can only be recruited from very specific landmarks
  • Raised from the dead, too, perhaps?

[im-mortal]

@Zalbardeon suggests using this artistic representation as a reference for unit card:

[Zalbardeon]

This would most certainly be available from a province such as Arkhan's Black Tower, Black Pyramid of Nagash, Gal Baraz and Nagashizzar.

[im-mortal]

But recruitable, raisable, or both?

[Zalbardeon]

It will be recruitable and raiseable, but bound by capacity obviously.

[Zalbardeon]

I've done all of the tablework for the Zombie Dragon. Will run some tests in custom battle to make sure animations etc look good.

[im-mortal]

It's been decided to use the Black Dragon unit card as a base instead:

[im-mortal]

Closing as #13 is merged.

[im-mortal]

Another revision of the unit card. Now using Moon Dragon as a base:

[im-mortal]