MongoDB driver should use goroutines to request all collections concurrently

[t-persson]

Description

When doing an event by id request in the MongoDB driver, it has to request all collections. This is done sequentially today and should be done concurrently using goroutines.

Motivation

Faster requests.

Exemplification

If the event is in the last collection in the slice, then the user would have to wait until all other collections have been queried before they will get the event they requested.

Benefits

Faster lookups for users.

Possible Drawbacks

We would hammer mongodb, but that should not be a problem.