Add support for speakers confirming their own presentations

This way we don't have to manually switch talk status twice. With this,
talk status is changed once (submitted -> pending). After this, the
speaker can confirm it him/herself which will move it (pending->approved).

Reserve list is still managed manually, but that should be seldom enough
that it's not a problem.
Add support for automatic notification of accepted/pending sessions

This will not actually send notification emails when the status of
a submission has changed. Instead, the updates will go on a queue,
which will then show up on the admin dashboard and can be sent from
there. The reason for that is to have a safety valve to catch manual
mistakes (as sessions are still changed from submitted->pending
manually).

The email will tell the user what the status is for he new session,
and what this status means, but nothing actually conference specific.
It might be worth adding some sor tof "welcome message" on a per
conference basis in the future.

The notification queue will automatically be hidden once the conference
end date is in the past.
Split SQL step in two

Can't do it in a single transaction due to referential triggers,
but the toolkit will always run them as one..
Really ugly workaroiud for the SQL update and transaction issue :O