This patch introduces a CivSpecific class for those specific structures that should be included in the {civ}.json files and listed in the civilization overview (“History”) page.
Previously there already exist a SpecialBuilding class, however, that one is tied to the template_structure_special,xml file, thus not usable, since not all structures that inherit from *_special are buildable, and since not all civ specific structures inherit from *_special. Therefore an additional class is necessary.
For the Roman siege walls, the class is inserted in the wallset file, which also shows up in the Structure Tree, not in the individual wall segment templates.
According to simulation/components/Identity.js, <Classes> is supposed to be listed below <Tooltip> but above <Icon> and <RequiredTechnology>.
[EDIT] Furthermore, changed the caption strings in the civ overviews from “Special Structure/s” and “Special Technology/ies” into “Specific Structure/s” and “Specific Technology/ies”, for consistency.