Feature/jsa/track slowdowns

@e0d @gwprice 
cf. https://edx-wiki.atlassian.net/browse/FOR-259

newrelic method traces were added for a few oft-used methods and some of the individual pieces of (deep) search.  verified these turn up in the newrelic instance for loadtest.

the other piece adds logging that should be useful in postmortem situations - it allows per-request correlation of unicorn pid, dyno, and request_id, and includes counts by type of objects loaded during the request by mongoid.  this logging is not enabled by default.