Feature diagnostics

Experimental.

Sometime we break key features on the website, and sometimes there's a perception that something is broken when it is not - Eg, we break a minor function that has little bearing on usage. The latter problem can create greater volumes of upset than it needs to.

To help cut the wheat from the chaff I propose this.

For each feature we build we should identify the key thing it does and sample some usage statistics of that key thing on to the diagnostic box. When the graph flatlines it means we've broken something. When talking about a _problem_ in retrospect we can look at the graph to decide if it had an impact on our users.
 
Eg, for the 'video' feature the critical thing is the ability to play it.