Event capacity should take into account registrants, not registrations

[if-owen]

Given that a single registration can contain multiple registrants, depending on the settings for that event, it seems that the event capacity should be tied to the number of registrants rather than the number of registrations.

As an example, if I create an event with a capacity of 10, I would expect that to mean that 10 people could attend the event. However, I am able to register more than 10 people to attend by allowing multiple registrants per registration. I am limited to adding 10 registrations, but not limited by registrants.