This patch:
* renames the `elephant_stables.xml` templates to `elephant_stable.xml` (without plural s), as well as their generic `template_*.xml` parent (cf. D1790/rP22322, D1860/rP22320, and D1890/rP22328)
* corrects all occurrences in simulation and map files accordingly;
* renames the stable and elephant stable audio files;
* also drops `pers_` from the `barrack.png` and `stable.png` icons.