Some clients aren't really capable of authenticating + some users probably
don't want to enter a password for the web interface. This option allows
clients on for instance the local network to connect without authentication.
For people who want to avoid the web login, or want to get around pairing
problems. This is also added because commit #e59a1a1 means that all
Remotes are now subject to auth, not just those with a user-agent name that
starts with "Remote".
the admin password
Changes the default for the admin password to be unset, by default only
allowing access to the WEB_ROOT files if accessed from localhost.
This also introduces a new config option to define a default playlist
folder. The default playlist folder is used by forked-daapd if the
playlist is not a full virtual path (simpifies creation of playlists
with mpd clients).
