WIP: Network File Storage: version 2

Network File Storage app supports accessing files over HTTP(S), Samba and SFTP. It has all the Samba app features, it does not cover some of the Sharing app features - sharing arbitrary folders, choosing user groups.

Samba app should be installed to be able use this app.

In principle, Network File Storage works by bind mounting all the shares found on disks into one folder /var/lib/freedombox/share_root. This work is done by the action script:
./actions/sharing2 scan-share-folders --debug
The main reason I chose this solution is that it allows to access shares over SFTP chroot. This bind-mounting solution needs still to be evaluated if it is a reliable way forward, major changes may happen during development.

Some features planned/considered: miniDLNA shares, read-only shares, run the scan-share-folders script during plinth startup and after disk mounts/unmounts, rename shares, sharing arbitrary folders,