Move our third-party script dependencies into js/lib/.

This move makes it easier to separate out our dependencies from the rest
of our code. As our codebase grows, this organization will help
considerably. It will also be easier to grep without including all our
dependencies.

The code up for review just updates the references to dependencies. It's
not worth showing the actual moved file contents, but for reference:

 rename reviewboard/static/rb/js/{ => lib}/csshover2.htc (100%)
 rename reviewboard/static/rb/js/{ => lib}/flot/excanvas.min.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/flot/jquery.flot.min.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/flot/jquery.flot.pie.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/flot/jquery.flot.pie.min.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/flot/jquery.flot.selection.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/flot/jquery.flot.selection.min.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/jquery-1.3.2.min.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/jquery-ui-1.6rc5.min.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/jquery.form.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/jquery.masonry.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/jquery.timesince.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/pngfix.htc (100%)
 rename reviewboard/static/rb/js/{ => lib}/ui.autocomplete.js (100%)
 rename reviewboard/static/rb/js/{ => lib}/ui.autocomplete.min.js (100%)

The pages in the UI that I tested continued to work. This includes the
dashboard, review requests, and admin UI.