new software: ProFTPd

Proftpd with sftp and virtual users

http://www.proftpd.org/docs/

Features

sftp only is enabled
partially uploadloaded are not visible thanks to HiddenStores ( in fact they are, but name starts with . )
5 failed login attempts will cause the host to be temporary banned

TODO

only password login is enabled. enabling SFTPAuthorizedUserKeys seems to break password only login
log rotation
make sure SFTPLog is useful (seems very verbose and does not contain more than stdout)
make it easier to manage users ( using mod_auth_web against an ERP5 endpoint or accepting a list of user/password as instance parameter )
allow configuring webhooks when new file is uploaded

depends on https://lab.nexedi.com/nexedi/slapos.core/merge_requests/41