Track error codes by number and class

[mheffner]

This removes the status code -> status name mapping and instead reports status counts by their code number (201, 404, etc). It was hard to keep track of what the string mapping names actually meant in terms of error code. It is something that should probably be handled with a display name at the graphing/presentation layer -- not in the metrics name. Also, this didn't scale well if you are interested in more codes than the mapping provided.

In addition to tracking per code, this will track per class of code: 2xx, 3xx, 4xx, etc.

[mperham]

+1

[technoweenie]

I don't know.... The problem with this is it could lead to an explosion in StatsD keys. Maybe there's just always a small, finite set of possible statuses though. Hmm.

I really want to just rip the statsd out and replace with ActiveSupport::Notifications, so it's easy to do your own thing here.