ammo system

* heads have abilities
* health and ammo shows in ui

src/main.rs

@@ -1,4 +1,5 @@
 mod abilities;
+mod active_heads;
 mod aim;
 mod alien;
 mod backpack;
@@ -116,6 +117,7 @@ fn main() {
     app.add_plugins(loading_map::plugin);
     app.add_plugins(sprite_3d_animation::plugin);
     app.add_plugins(abilities::plugin);
+    app.add_plugins(active_heads::plugin);
 
     app.init_state::<GameState>();