Add ability to name meetings

[malini]

Is your feature request related to a problem? Please describe.
It would be nice to be able to name the meetings you're booking someone for. Someone requested this when I gave them my booking url and I agree!

Describe the solution you'd like
When I go to a booking url, I'd like to be able to suggest a title of the meeting. Perhaps in this dialog:

As the receipient of the booking request, I'd like to be able to see that suggested meeting title and edit it, perhaps in this dialog: