Add option to include guest information in back-office confirmation emails

Problem: when you send a confirmation email from the back-end after registering a participant, or editing their booking, it only includes the information for the 'current' participant (ie, just the lead booker). It does not include any 'additional participants' (guests) linked to their registration.

Solution: suggested CiviCRM core patch to add a checkbox to 'include guest information' for confirmation emails for participants that have guests attached to them. This would include the guest information int he email, as though it was from a front-end booking.

ie: IF the booking has additional participants, display a new checkbox:

If the checkbox is ticked, then add in the guest information, in the same way as a 'front-end' registration would add their information.