Drop python2 support This mostly consists in removing the dependency on "six" and updating the code to use only Python3 idioms. Notice that we previously used TemporaryDirectory from cubicweb.devtools.testlib for compatibility with Python2. We now directly import it from tempfile.

addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile