Minor cleanup; soft decommission of 'RPM'

Fixed the following: typos, minor tweaks, code formatting, dropping legacy 'RPM' name in favor of nothing at all or 'APM' (and even then with New Relic One already here, I'm just in favor of simplifying the namespace to just 'New Relic'. This patch is the beginning of that for D7's release so we can close the book on it but let sites run this module with that proper context through the life of D7.

For reference, RPM means "requests per minute" and this module became more of an APM module. Here's the history and official glossary definition for New Relic's "RPM":

The term RPM usually refers to the number of requests per minute your application receives from users. This is usually the same as CPM (calls per minute).

For some New Relic products like APM and Browser, RPM is also part of the product URL; for example, https://rpm.newrelic.com. This usage originally referred to Rails performance management because the first New Relic agent monitored Ruby on Rails applications. New Relic monitors many languages and systems far beyond Ruby now.