wall template improvements and some related changes

[Nescio0]

• wall templates:
  • adopt systematic naming scheme for byza wall templates
  • purge unnecessary lines
  • adjust footprints, obstruction sizes, status bar heights (cf. rP23609)
  • increase the number of turret points of medium walls from three to four and long walls from five to eight (cf. rP24019)
  • add a number of turret points for each gate as looks good (cf. rP24020)
  • caro and norse wall towers get four turret points (cf. D2769)
  • differentiate wall costs of various civs
• add wall-related civbonuses (cf. maur_walls.json)
• group civbonus files in civbonuses/ folder (cf. rP22083)
• clean up civbonuses and {civ}.json files (cf. D2720)
• fix unit builder lists

The “Fortress” random map is great for playtesting, as is placing entities in Atlas. I think this patch is now complete and correct, thus ready to be reviewed. (@s0600204, @StanleySweet, @wackyserious? I realize it's quite large.) And a screenshot: