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.

[akalata]

100% this, but I think we should keep the registrant limit per registration.

Use case: Tournament Sign-Up
An individual is responsible for signing their team up for the tournament. Team members are individual registrants, linked under a single registration.
Registration limit: 16 teams
Registrant limit per registration: 8 people per team max (could also use min to enforce team size)

Use case: Seminar Sign-Up
An individual wants to reserve one or more seats in the seminar. The room size fixes the seminar to 100 audience members.
Registration limit: no limit
Registrant limit per registration: no limit
New limit needed: Maximum registrants per event

[akalata]

This is actually a duplicate of #130