Add Session Titltes

Rather than making people guess what delights will be lurking behind
the Google Docs links, add titles for them all (Painstakingly collected
by Gemma)

This makes the cells too big, so also fall back to simple list styling
within each td.
Remove 'Propose a Session'

Now that the event is over, the page should just list what happened
— we no longer need the explanations on how to propose sessions etc.