Sort models in gcodeplater to print smaller ones first

gcodeplater.py

@@ -72,6 +72,8 @@ class GcodePlater(Plater):
         with open(name, "w") as f:
             models = self.models.values()
             last_real_position = None
+            # Sort models by Z max to print smaller objects first
+            models.sort(key = lambda x: x.dims[-1])
             for model in models:
                 r = model.rot  # no rotation support for now
                 if r != 0: