add python-tk, backend for plot with matplotlib in python

Miguel Rodriguezrequested to merge
so77id:master into master

When you use plot from matplotlib in this docker image get this error:

screen shot 2017-08-14 at 20 57 09

This error is solved installing python-tk. For this specific implementation, the error was solved adding python$PYTHON_VERSION-tk \ in apt-get packages installations.

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