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 slapos.core!41 (merged)