[IMP] event: Split Ticket: registration are now for one attendee only.

Registration are now for one attendee only. When buying several seats for an event
you have now one registration for each attendee.

event: nb_register field is removed; as well as unnecessary user_id and it subscribe /
unsubscribe behavior. Also slighly cleaned some views.
event_sale: do not auto confirm registrations linked to a draft sale order. Note: strange
origin is a char field, not a sale_order_id. Added a small wizard to edit attendees
data when confirming a sale order containing event related lines.
website_event: when buying free tickets, ask for attendee details. Added template,
controllers to handle that behavior.
website_event_sale: when buying tickets, ask for attendee details. Events ecommerce
should be better integrated with online events, using inheritance to add details
instead of being very different.
[IMP] payment, website_sale: better control of sale order confirmation in ecommerce.

Auto confirmation is now controlled by a field on the acquirer
that proposes to confirm
- at payment (Pay Now button on ecommerce)
- at payment confirmation (transaction feedback)
- never

Also fixed the state of tx for transfer transactions that was modified
for debugging in a previous task but not reverted.
[IMP] website_sale : Don't show shipping address when only services are into shopping cart.