Multiple changes.

- Changed the ajax data loading to a method instead of using the DataTables ajax methods.  This should allow easier error handling.
- Also, buy moving the AJAX to an external method, we are now able to break apart the response to multiple items such as categories, feed, hiring centers, etc
- Added an initial filter to hide the "Apply in person" jobs
- Added the "hiring center" drop-down
- Moved the event handlers to the DataTables initComplete method
- Fixed issue where category filter wasn't working properly and was applying to all columns instead of just one
- Fixed issue where search term was not finding matches outside the name column

 - Added additional space above the table to make the presentation cleaner