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).
