Initial conversion to Segment.io

This moves us to Segment.io which makes piping our analytics data to other providers super easy. The idea would be that we setup Segment.io with Google Analytics and in the future if we choose more services or a replacement service, switching will be easy.

It needs to be easy because I'll be adding JS event tracking to most user interactions in the neat future. This gives us a single API to work with instead of 20 :)

P.S. **Do not merge.** (Waiting on Segment.io Key)