Reusable invitation lists (submodule)

I thought it would be a very useful feature to be able to easily reuse past invitation lists. I know the module can already export lists and statuses as CSV, but that isn't very friendly for the end user who just wants to load up a past list.

This module will add a block right above the "Add guests" block (on /rsvp/%rid/attendees). A select widget will be present, loaded with all invitations you've either created or have been set to a moderator for (unless you have the 'administer rsvp' permission, then you'll see every invite). Select the invitation you want and press load. The page will refresh with the "Add guests" textarea pre-populated with the entire invite list from the selected invitation.

Some questions:
1. Do we want the ability to select only certain invitees (ones who've accepted, not accepted, responded, etc)?
2. Do we want additional permissions created to allow certain users to use the lists of any invite?