Add collect_full_address

Adds the option to collect attendees' full addresses, and also adds that ability.
Long term, I'd recommend just having a text field and then doing some basic address validation.  There are open source libraries for this; one of the teams where I work does this so I'll ask them what they use.  Having just a text field is probably a little cleaner since it reduces the number of form fields and such, so long as we're making sure that people are actually entering something that looks like an address.