Dashboard should have more registration information

[domfarolino]

Beyond returning everything, the dashboard API should return:

• The number of registrants
• The number of registrants with verified email addresses
• The number of registrants who have been sent the confirm-attendance email
• The number of registrants who have either confirmed/denied their attendance

Previously this would be estimated by looking at the return table of information, but we can be exact by returning the count along with the data, and displaying that too in the front end.

/cc @noahbass

[noahbass]

👍 Excellent. This is perfect.