adapt message model

-  add column "instance"
-  make sender_email and sender_name optional
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
emit message event and notifications
enforce email_sent and force_resend
actually commit stuff to the database
allow to format email subject and body
add simple message wrapper
use message.send in massmessage
use message.send in message controller
update help texts
remove email specific checks from auth.user.message
fix typo s/recieve/receive/
render message template in event listing