2.1.5.6 assorted updates

Since folks seem to be adding all the other 2.1.5.6 goodies, here's the
rest of them! (I also updated the changelog with the Catholic
schism/Crusade change, since someone forgot...)
Updated Nubian buildings to match PB model

You might want to eventually tweak the troop totals, but it works for
now.
Merge pull request #182 from thefinestsieve/beta

2.1.5.6 assorted updates