Tracking logs

`feedback.shown` is not implemented, since it is already implied by a `problem.attempted` event. There is no other way to trigger a feedback.

It would be nice to add an `item_id` to the `feedback.closed` event. It might be a good idea, and relatively easy, but that would include giving IDs for each feedback, meaning some extra work and code.


Agreed that this function belongs in xblock core. However, I do think some additional work needs to be done to establish some sort of shared key between server and client, so that the endpoint cannot be easily abused. Just a thought.