Live Events API

API Endpoint for getting the live events at a specific time.

Parameter is UTC timestamp (will be normalized to last Monday) - this allows for deterministic cache keys. I do need some help with cache-busting, though. I'm not sure how to clear them, though - the clearer is passed a list of keys. Is there a way to translate those to the start times without database queries (which I assume shouldn't be done there)?
Probably should be `ApiEventsLiveController`, or maybe `ApiEventsCurrentController`, since that sounds more 'date-like' than 'live'.