Bug fix and improve MCTS and others

• Fixed error with mean and std
• Improved MCTS.
  1. Fixed a bug of starting with start_node;
  2. Fixed the miscalculation of mean and std;
  3. Added timeout to prevent infinite-loop.
  4. Changed output format in mcts.py
  5. updated and tested mcts.py
• Refactoring (env -> worlds)
• Change AP ('before_but_close_to_stop_region' --> 'close_to_stop_region')

backends/mcts_controller.py

@@ -106,4 +106,4 @@ class MCTSController(ControllerBase):
         if self.debug:
             print('Btw: %s' % str(p))
         self.mcts.tree.reconstruct(node_after_transition)
-        self.set_current_node(node_after_transition)
\ No newline at end of file
+        self.set_current_node(node_after_transition)