Allow proposals authors to indicate "talk I want to give" vs. "talk I want to hear"

[h-lame]

There were a few talks on the Ruby Manor 4 vestibule that were topic suggestions rather than concrete proposals. We allowed this on the mailing list for RM:Classic and RM:Harder, and we did talk about it for ru3y manor, but much like #29 we never got round to it. Also like #29 it's not clear what the UI or workflow around it might be:

• can someone take it over and turn it into a talk?
• how would that fly when it comes to anonymization?
• should they just propose a new actual talk instead?)