jQuery, Header, and Footer 2/4

Merge second! (After jQuery, Header, and Footer 1/4: https://github.com/otwcode/otwarchive/pull/1102)

Changes the site header to have dropdown menus.

Issue 2933 Main Navigation Implement drop down menu accessible with keyboard and without javascript: http://code.google.com/p/otwarchive/issues/detail?id=2933