Replace hard-code email address in online event registration forms with a reserved profile, and allow online event registration forms to NOT collect email addresses

At present CiviCRM forces the email address field into the online event registration form, and does not allow online registration w/o requiring user to submit an email address. If an email address is also included in the profile added to the event registration form, then that email address field is suppressed the profile form.

CiviCRM should be amended so that instead of adding the single email address field into the form it requires the user configuring the event registration form to include a profile which contains an email address (required) OR first + last name fields (both required). A new reserved profile will be provided which can be used for this purpose - but users will be free to select any profile which meets the requirement.

This is the master issue for this improvement. See sub-issues for details.