always hide #nav_dummy

#nav_dummy should be removed by diazo. If this is not
the case it sometimes breaks the layout. To avoid that
we don't display it at all.
change model.Message to be less specialized for email
change massmessage to be less specialised for email
clean up remaining massmessage preview code
add find() and all() in model.Message
add message view
add message entity_url
create message events
hide message events from event streams
message tab in dashboard
move send from model to lib
add reply_to in lib.mail
use reply_to instaed of email_from
emit message event and notifications
enforce email_sent and force_resend
actually commit stuff to the database
allow to format email subject and body

this removes possibility to format the message itself,
e.g. using {name} as placeholder
add simple message wrapper
use message.send in massmessage
use message.send in message controller