[pkg] various fixes - add missing files to MANIFEST - exclude doc/changes from dh_installchangelogs (it's a directory, which dh_installchangelogs doesn't expect) - fix doc build in debian package

usr/bin/cubicweb-ctl usr/bin/
usr/lib/PY_VERSION/*-packages/cubicweb/cwctl.py
../cubicweb-ctl.bash_completion etc/bash_completion.d/cubicweb-ctl