[skeleton] Have setuptools install data files
Just add `include_package_data=True` as recommended by
`setuptools documentation`_ as this appears to be the simplest way to handle
this.
Related to #13001466.
.. _`setuptools documentation`: \
http://setuptools.readthedocs.io/en/latest/setuptools.html#including-data-files
missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)