Identify slow requests

[jonodrew]

I'm not completely happy with this yet.

I've written some helper methods to grab all of the 'things' a member is attending and find them once, when the controller method is called. This replaces the map loop that generated two queries per event.

However, I think there's some clash here. The set of Event, Meeting, and Workshop ids will have some overlap and the tests will therefore be flakey. Advice welcome