Added statsd and started on the instrumentation
Renamed the PDF instrumentation names

In order to make them clear and obvious what they are for.
Implemented the stats collection for statsd

Reorganised the methods and made the obvious what their functionality is.
Merge pull request #435 from ministryofjustice/pdf-metrics

PDF metrics
Upgraded rails to 4.1.15

Due to security issue
https://groups.google.com/forum/#!topic/rubyonrails-security/M4chq5Sb540
updated brakeman gem to 2.6.2