Created a help menu that replaces the old support menu. This new help menu allows pages to offer page specific help. The help menu also provides a key binding's reminder modal that is accessable by the '?' keyboard shortcut. This included adding the library QuestionMark.js(http://impressivewebs.github.io/QuestionMark.js/) to reviewboard, and making sure that the modal created using this library only appeared when a page has key binding content.

This change has been tested on Chrome, Firefox, Safari and IE. 
Testing involved making sure that the links in the menu led where expected, and that the menu correctly displayed page specific content. It also invloved making sure that the key-bindings modal was accessable via the keyboard shortcut '?' in screens with keyboard shortcuts, and otherwise was not accessable.