Altered creation of connections to mongo to allow for replications sets to be defined in config.js

This is a response to the Onur's port on Aug 21, 2013 at http://support.count.ly/discussions/problems/150-problem-upgrading-to-latest-version-1306-error-cannot-find-module-homeoilcountly-serverfrontendexpressappjs 

I was also unable to find a connection string that would accomplish this.  The changes were based on documentation at https://github.com/kissjs/node-mongoskin#dbserverurls-dboptions-replicasetoptions and the existing county code.