Update header nav to include Help dropdown

#### Story ####
- https://www.pivotaltracker.com/story/show/67683668

#### Notes ####
- updated Help link in main header nav as a dropdown menu with links to [Contact](mailto:bonnie-feedback-list@lists.mitre.org), [Issue Tracker](http://jira.oncprojectracking.org/browse/BONNIE), and [User Guide](https://github.com/projecttacoma/bonnie/blob/update_header_nav/public/resource/Bonnie_user_guide.pdf)
- updated user guide files in <code>/doc/</code> and added copy in <code>/public/resource/</code> for linking in the Help dropdown menu

#### Screenshots ####
- default, unselected Help link
  - ![screen shot 2014-04-15 at 2 33 52 pm](https://cloud.githubusercontent.com/assets/456952/2711311/5f7dcadc-c4cc-11e3-8d33-61cff8282855.png)
- toggled Help link
  - ![screen shot 2014-04-15 at 2 34 05 pm](https://cloud.githubusercontent.com/assets/456952/2711312/5f7e2d7e-c4cc-11e3-9846-3667b1879556.png)