Add initial statsd calls for metrics collection

[robhudson]

Description

Following the ADR to Use statsd for metrics collection, this issue identifies some good initial areas for us to start collecting metrics within bedrock.

Also, after surveying the current state of Python packages that enable statsd collection, markus is the recommended library to use as it is the most up to date, written for an used within Mozilla currently, and offers a broad support of various backends.

Initial metrics to add:

• [ ] WhatsnewView, FirstrunView timing
• [x] Middleware to track status codes