Don't need registrantId & authkey params if logged
Adapt redirections to main page
Pass auth GET params to template
Remove already registered page
Hide 'Modify' button from guest registrants
Redirect modify/ to register/ if not registered
Fix params passed to checkout page
Redirect to main page on registration closed
Do not check for currency not selected
Change registration closed message
Sort imports
Redirect to main page on registration full
Fix body title on registration modification