Added basic month/year filtering to stockings

This has a failing test.  I'm opening the pull request to discuss it.  I've added a select to the page and its onchange fires javascript to submit the form.  However, I don't think rspec understands this and so it may not be waiting for the page to reload before looking for last month's stocking.  Thoughts?
Added this bit for user convenience, but I think rspec might not understand that changing the select reloads the page.