Fix map schema (#3138)

Schemas/mapfile.yml

@@ -5,11 +5,7 @@ meta:
   author: str()
   postmapinit: bool()
 tilemap: map(str(), key=int())
-grids:
-- settings:
-    chunksize: int()
-    tilesize: int()
-  chunks: list(include('chunk'), min=1)
+grids: list(include('grid'), min=1)
 entities: list(include('entity'), min=1)
 ---
 chunk:
@@ -19,6 +15,12 @@ entity:
   uid: int()
   type: str(required=False)
   components: list(comp())
+grid:
+  settings:
+    chunksize: int()
+    tilesize: int()
+    snapsize: int(required=False)
+  chunks: list(include('chunk'), min=1)
 
 # Example
 # meta: