referrer tracking

This tracks which page an individual user came from to reach the site as well as which page they came from to get to the sign up form. It stores a raw URL, exportable to csv, that we can analyze later.

This is useful because if a user came from the apply page, it means they are probably interested in applying, etc. If they came externally from Google searching for the keywords "job opportunity", we might be able to use that when reaching out to them too.
These column header names could be improved, but nothing is coming to mind.  Let's wait to see if someone has a better proposal once we actually start to use this.