Game state register (#1341)

* Added a gamestate register helper

Added a gamestate register helper

* Update mod_interface.js

src/js/mods/mod_interface.js

@@ -367,6 +367,14 @@ export class ModInterface {
         });
     }
 
+    /**
+     * Registers a new state class, should be a GameState derived class
+     * @param {typeof GameState} stateClass
+     */
+    registerGameState(stateClass) {
+        this.modLoader.app.stateMgr.register(stateClass);
+    }
+
     /**
      * @param {object} param0
      * @param {"regular"|"wires"} param0.toolbar