[Python] Any buffer line starting with ERROR should raise an exception

[magoorden]

The error pointed out in #60 was not caught by the Python driver, i.e., it just continued execution the Python script without dealing with this error.

Therefore I suggest that any error from the Arduino should raise an exception in Python. Then it is up to the designer of the experiment to handle this exception, otherwise the Python code stops and doens't force the demonstrator to do things it does not want to.