Remove performer question from ticket request

A requester won't know whether or not a they have been selected as a DJ
when tickets become available, so don't ask them.
Add vehicle camping requested question to form

We want to know if a ticket requester is asking for a car/RV camping
spot so we can relay that information appropriately.
Change ticket maximum based on chosen role

Different roles have different ticket maximums. Have the maximum
dynamically change based on the role chosen.

We don't implement server-side checking since the requester could lie
about their role anyway, although we may add it in future.