Add a user-selectable agenda

[shaib]

It is much more convenient for attendees if they can prepare a "selected agenda", showing only the presentations they're interested in. This should have some sort of persistence, so it stays on their mobile browsers when they're offline (and when they're online, of course).

It should present a personalized aganda.

Bonus point: Support more than one presentation per slot
Bonus point: Support setting some sort of reminder or calendar

That's just what comes to my mind. Some client-side expertise seems required.