Add a party alliance roll option

[pedrogrullada]

It would be useful for automating features like Blessed Counterstrike that grant a critter weakness against your allies' Strikes, or for features with selective difficult terrain, like Nature's Reprisal, once difficult terrain support is in full swing.

I'm envisioning something along the lines of self:alliance:opposition, self:alliance:neutral and self:alliance:party.

[pedrogrullada]

Forgot to mention it, but closed by #16643