Renamed the Gates class to Gate, LongWall to WallLong (cf. WallTower), and StoneWall to Wall, to match their template file names. Adjusted AI code, technologies, and templates accordingly.
Entity build restrictions:
    renamed Apadana to Palace;
    replaced UniqueStructure with IshtarGate and TempleOfVesta.
    added Council to the (unbuildable) spart_gerousia.xml, since it's functionally identical to athen_prytaneion.xml.
Introduced the following classes:
    Council, IshtarGate, Library, TempleOfVesta, and Theater, to match their build restrictions.
    WallMedium and WallShort, to complement the already existing WallLong and WallTower classes.
    Stoa, TempleOfMars, and TriumphalArch, for completeness.
Made the ArmyCamp, Colony, Gate, Lighthouse, Naval, Palace, Palisade, SiegeWall, and StoneWall classes visible.
Deleted the now unused Apadana, Kennel, SpecialBuilding classes.
Removed the Village class from outposts and palisades, because those are not supposed to count towards the phase technology requirements.
    Slightly rephrased the phase technology requirements tooltips.
Corrected the <GenericName> of the various palisade files.
Updated Structure tooltips from D2578 that have not already been committed elsewhere.