Venue Request Form: add fields to help with deployment

[racheljsmart]

I'm hoping that adding an optional "colocated_with" field to the venue request and revision invitation will reduce the amount of time it takes to review the requests and deploy with the right venueID.

field name: colocated_with
field desc: "Please provide the name of the conference, organization, or academic institution with which your event is colocated. If your event is independent of a conference or organization, you can leave this blank or write 'independent'".

Maybe we can also add this second field.

field name: previous_venue
field desc: "If possible, please provide a link to the previous iteration of this venue on OpenReview."