Reservation detail enhancements

[cbellone]

Some enhancements suggested by event organizers:

• send tickets to one or more attendees
  change the behavior of the current button, open a dialog to select which ticket(s) to send. Default selection: all

• add email log, with the emails sent for the reservation
  this way it would be easier to check if an email has already been sent or not

• add check-in log for each ticket (popover? list?)

[syjer]

note: I'm taking care of the email log in the reservation.

Will need to add a new column reservation_id to email_message (not a fk, nullable).

In term of UI, as only the new emails will have the reservation_id -> if the reservation has no email log, it means it's an "old style" one -> we show a message. In the other cases, we can show a message that warn that not all the emails will be attached to it.

[cbellone]

implemented.