Separate twisted-specific configuration from WebConfigurationBase class
This is in preparation of dropping the Twisted web server backend.
We thus draw a clearer line between what's specific to twisted from
what's generic by moving WebConfigurationBase class into
cubicweb/web/webconfig.py and only keeping twisted-related in
AllInOneConfiguration (still living in cubicweb/etwist/twconfig.py).
etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances