Add a __main__ to cubicweb
This avoids calling cubicweb-ctl relatively in tests and could be useful
in virtualenv.
This is just a copy of bin/cubicweb-ctl file, which should probably be
generated from a setuptools entry points.
addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile