Add employer location information

This is an attempt to add the employer location information requested in issue #11.

I added this as a post_save signal for Job.  This way location data can be slowly added to the DB as people edit jobs.  If we wanted to globally update existing employers, this could be modified to be a post_save signal on Employer. 

The location information can be added to any template by passing the Employer object to the included location snippet.  

The city, state and country are stored as strings using the existing Employer model.  Further enhancements could include fetching the latitude and longitude for the city from Freebase and using that in some type of map display.