Horses added

Horses added to the warband manager in the form of items.
I think its going to be easier to manage horses as items due to how they affect stats. The horsemanship training is also an item so just add them to the soldier or unit which is to be mounted once you have purchased/added them from the vault.
I've also added riderless horse as a soldier type with zero cost but the horsemanship training items which affect the riderless profile are not factored in - this requires changes to the code which I am not in a position to change at the moment.