[Feature Request] Heirgamenon improvements

1) Tell what element the spell is and what spellbook and/or research is needed.

2) Allow it to be searchable.

3) I think it was the Great Mill - anyway there was a building that one of my cities could build and another city could not.  The building description in game and in the Heirgamenon were exactly the same - neither listed any pre-reqs for the building.  Please list all pre-reqs for all buildings.