Feature/rails3 access keys

implement parts of https://www.openproject.org/issues/2221

* add keyboard shortcuts (more functions menu, preview, edit, next in list, previous in list)
* add access_keys (more functions menu, project search, fixed edit on work_packages)
* added items to keyboard shortcut help modal
* moved some affected modules into the OpenProject namespace
* changed default help-url in main menu so that it points to a valid url