Spike to find an alternate to ganglia for diagnostics

`./px.gif` services all requests.

I use the Play cache plugin to increment counters against a key formed from the current hour + minute.

So a `GET ./px.gif?type=js` at 8:30pm will increment a key `js.2030` by one.

Each key dies after 300 seconds.

A scheduled job can shuttle the data to CloudWatch one a minute.
Use a singleton for maintaining the Metric state
Job to push diagnostics data in to CloudWatch
Protection from unspecified error type
Use it's own timing metrics
Ability to count lots of metrics
Remove the cache plugin
Do a proper job of clearing the map
Batch the metrics to CloudWatch
Only log the data for widely used devices
Only load data to CloudWatch in production
Move the Metric.reset to a future in the load job
Typo
Log only on PROD
Split the error type from the message

For some reason we were doing `px.gif?js/message=...`

Now we log errors to the server like so, `px.gif?type=js&message=...`
void most of the Metric functions
Merge pull request #2194 from guardian/diagnostics-sans-ganglia

Diagnostics sans ganglia