Matplotlib show_message encoding error

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.