Add optional support for new relic

On our current project we have run into an issue where:
- New Relic instrumentation wasn't working for us
- With a fix for New Relic Instrumentation it was too much and we wanted to turn off Cequel gem instrumentation and create our own.

This PR adds a change to the cequel.yml file to support a ```newrelic_enabled: boolean``` parameter and a check in the cequel/record/railtie.rb initialization for this new param.  If the param is false we completely bypass importing NewRelicInstumentation

To get instrumentation working we trace :execute_with_consistency

-Jeff Holland
I would default all these to true, to not change existing behavior, which is "on if new_relic gem is found".