Improve directory structure of maps

- Each map will have its own sub-dir, containing
  - `map.conf` (used to be `<map_name>.conf`)
  - `map.mts` (used to be `<map_name>.mts`)
  - `screenshot.png` (used to be `<map_name>.png`)
  - `skybox_<n>.png` (used to be `<map_name>_skybox_<n>.png`)
- The `ctf_map` post-processing actions for maps has been moved into a dedicated shell script `setup_maps.sh`. This script appropriately renames all the textures to while copying them over to the mod's textures/ sub-dir. e.g.
  - `cool_map/screenshot.png` ---> `cool_map.png`
  - `awesome_map/skybox_2.png` ---> `awesome_map_skybox_2.png`

update.sh

@@ -1,8 +1,17 @@
-git pull &&
-cd mods/crafting &&
-git pull origin master &&
-cd ../ctf/ctf_map/maps &&
-git pull origin master &&
-cp ./*.png ../textures/ &&
-cd ../../../.. &&
+# Update capturetheflag
+git pull
+
+# Update crafting submodule
+cd mods/crafting
+git pull origin master
+
+# Update maps submodule
+cd ../ctf/ctf_map/maps
+git pull origin master
+
+# Run post-processing actions for maps
+cd ../../../..
+./setup_maps.sh
+
+# Run build.sh
 ./build.sh ../games/capturetheflag