Now placing units on walls no longer interferes with the opening and closing of gates (D1418/rP23710, rP23714, D2775/rP23731), it becomes possible to add visible garrison slots to wall tower as well, similar to medium and long wall segments. Advantages are that it looks better, is more realistic, and helps functionally differentiating wall towers, which are wall segments, from free standing towers (which are more expensive (100 wood + 100 stone), have a build limit of 30, and a mimum distance of 60 in between).
This patch:
* Allows brit and gaul wall towers to be garrisoned, just like those of other civs.
* Increases <GarrisonHolder/Max> from 2 to 4, because wall towers tend to be square. (For comparison, the smaller defense towers have 5, iber 8, and maur_tower_double 20.)
* Moves the wall tower attack into a new template, `template_structure_defensive_wall_tower_attack.xml`, which is used by those civs (athen, brit, mace, maur, sele, spart) that have wall towers which have a closed room instead of an open platform on top; effectively this patch changes nothing for those.
* Those that have a flat roof (cart, gaul, iber, kush, pers, ptol, rome) get four visible garrison points on top. Because garrisons are now visible, the garrison flags are removed from their actor files.
* rome city wall and siege wall have visibly room for eight, but get only four, because they don't cost more than those of other civs.
* cart gets eight slots instead of four, because it's twice as expensive, and visibly larger: {F1402262}
* [EDIT]: The cost of the visibly garrisonable wall tower is reduced and made proportional to its health (cf. D2621/rP23713), whereas the ranged attack wall tower keeps its old cost.
See also D2477, D2760, D2783.