Checking and Fixing URLs in the data

Our contact dataset contained a number of URLs about where the FOIA-centric webpage for that agency/department and the FOIA request form URL. 

Unfortunately a number of those webpages didn't work (returning 404 errors, or worse). 

This pull request contains a script to run the URL checker (we'll likely need to do this periodically). It also contains fixes for almost all the broken URLs. 
Should this be an empty string?