JITSI_SCALE unset -- "normal" core installation
JITSI_SCALE=client -- Omit the JVB component, the Jitsi Scale servers
take over
JITSI_SCALE=server -- Omit anything but the JVB component to install a
Jitsi Scale server
There's no need to extract the entire Jitsi tarball into
/federated/apps/jitsi - we only need gen-passwords.sh
Also document what the tarball in lib/files/jitsi is and
where it comes from.