Matplotlib show_message encoding error

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Issue #57 invalid
M. Gronle created an issue

If the polar_demo.py script (matplotlib folder) is executed and a zoom is done, the displayed coordinate information contains greek letters. They raised an UnicodeError in backend_itom.py (def set_message). A workaround fixed the exception, however the special characters are currently encoded as hex-numbers. Maybe, it is possible to really display them.