Users should be able to edit job postings.

Also ensure that job searching in controllers/services is appropriately scoped.
Add sponsors table to schema.rb
Don't clear the table header when updating the jobs table
Show the "no listings found" message when no jobs are returned on an AJAX request.
Jobs should expire 30 days after posting.
Extract the events bar into a partial
Initial form and label cleanup
Rearrange the top right nav to show a login button and/or job posting button, depending on context