- add cronjob for splash_sync (every minute for debugging; to be
  increased)
- add redirection for unsplashed users in queen.enter, remove it in
  queen.leave
- add /etc/splash.sh to centralize functionality used in
  /sbin/splash_sync and /www/service/*splash*
- make splash_sync to use a transactional update approach: insert
  iptable rules for all splashed MACs into a new chain, then replace
  old and new chain; this avoids downtime even if splash_sync is slow
- remove allowed services for splashed users; this is intended to not
  move old cruft over to new code; if any of the those services shall
  be reenabled, it should happen in /etc/firewall.user
- make /sbin/splash_sync aware of the current state of FSM inetable
  (read via /sbin/fsm with optional command line override); this
  allows to unconditionally call splash_sync via cron
- add locks to all places where the splash state is touched
- remove multiple escaping/quoting/encoding problems in splash cgi
  scripts
- reenable link to the page the user initially demanded in
  /www/service/cgi-bin/splash_click

This patch splits the single uhttpd instance into two uhttpd instances
with www root /www/<servicename> for the following purposes:
- service :: self-service / debugging / status.xml
- redirection :: use for splash/robinson redirection

The uhttpd uci config is adapted: by default all instances declared
there are disabled; They shall be enabled by the FSM inetable. To this
end a listen_http directive will be added and the config type will be
changed from 'disabled' to 'uhttpd' by state transition scripts.