Add invisible FOBs (#504)

Co-authored-by: Raffson <Raffson@users.noreply.github.com>

resources/layouts/buildings/invisiblefob1.yaml

@@ -0,0 +1,14 @@
+name: invisiblefob1
+generic: true
+tasks:
+  - InvisibleFOB
+groups:
+  - FOB:
+    - name: fob1 0
+      statics:
+        - fob1 0-0
+      unit_count:
+        - 1
+      unit_types:
+        - "Jerrycan"
+layout_file: resources/layouts/buildings/buildings.miz