Level class created and gravity editable.

tilorswift/js/events/TilorswiftEvent.js

@@ -14,6 +14,8 @@ const TilorswiftEvent = {
     NEW_TERRAIN: 'newTerrain',
     NEW_TERRAIN_CLICKED: 'newTerrainClicked',
     TILESET_SELECTED: 'tilesetSelected',
+    MENU_GRAVITY_CLICKED: 'menuGravityClicked',
+    GRAVITY_UPDATED: 'gravityUpdated',
 };
 
 export default TilorswiftEvent;