Help dropdown menu, moved version info to it

Refactored help menu in top right to be a dropdown menu, exposing the old help link and the version info modal popup.

![Screen shot 2013-01-22 at 3 08 49 PM](https://f.cloud.github.com/assets/228715/87945/36f34466-64d8-11e2-9b26-8e2d038dc8ca.png)

Some quirks:
- I wanted to define the modal statically in `templates/partials/topbar.html`, but was having trouble with making it modal - it would show underneath the modal greyout overlay. I changed it to use the dynamic approach as seen in `static/js/ux-views-actionmenu.js`.
- I did not use the action menus because I wasn't dynamically creating the menu, it is a static creation. Therefore a simple backbone view made the most sense.