Allow admins to update locations

This commit includes the following features from the standalone interface:

- ability to delete a location, with modal window warning
- ability to dynamically add fields via JS for contacts, faxes, phones, address, mail address, websites, emails, and admin emails
- CSS styling for edit location form
- admin and super admin authorization to control who gets to see which locations

Other changes:

- move custom JSON errors when rescuing from Rails errors to a controller concern within the API namespace so that they don't get triggered within the admin namespace.