Setting ticket types correctly when changing them

[karianne]

When a person get all talks refused, the ticket type is changed. This should also update other fields in registration:
free_ticket = false
price = {early bird-price | full price}

[karianne]

Ticket types got some very much needed love (and tests!) in rootsconf - might want to steal.

[jhannes]

Some of the most important parts from ROOTS:

https://github.com/rootsconf/rootsconf2011/blob/master/db/migrate/20110123171436_create_ticket_types.rb
https://github.com/rootsconf/rootsconf2011/blob/master/db/migrate/20110123181058_insert_ticket_types.rb
https://github.com/rootsconf/rootsconf2011/blob/master/db/migrate/20110123185859_rename_ticket_type_old.rb
https://github.com/rootsconf/rootsconf2011/blob/master/app/views/users/_form.html.erb#L81
https://github.com/rootsconf/rootsconf2011/blob/master/app/models/user.rb#L63
https://github.com/rootsconf/rootsconf2011/blob/master/app/models/user.rb#L125