Remove non-attendee talks from All Talks view

[martian-a]

At the moment this view includes pre-organised/administrative stuff like meals and the opening/closing talks. Update the view to use Talks.all_attendee_talks, which filters out the mealtimes, etc.

Consider adding a second list to the bottom of thr page that includes just the mealtimes, etc., sorted on order of occurrence (rather than alphabetically).