add python_gear block (to execute python command each given cycle interval)

get the WaitPythonCommands return (semaphore error code) to quit python_iterator loop when semaphore is destroyed

Wait the debug thread has terminated before freeing PLC to avoid random segmentation fault.

Store working directory to globals copy, in order to be used in runtime.py.

Add try/except in wx_evaluator to get and print exception when command failed and unlock in all cases to not block the python thread