Adding drop downs to Boot Camp, Blog, and About menu items.

Dropdown menu items are:

* Boot Camps
  * About
  * Future Boot Camps
  * Map
  * Calendar
  * Past Boot Camps

* Blog
  * Recent Posts
  * All Posts

* About
  * FAQ
  * Sponsors
  * Team
  * Contributing
Make it so the dropdown caret only highlights when the menu is open.
Moved the About menu over next to Home.
PLoS ad
Merge pull request #209 from gvwilson/master

Blog post about PLoS ad
Merge pull request #205 from jiffyclub/nav-dropdowns

Adding drop downs to Boot Camp, Blog, and About menu items
Blog post about teaching commercially
Merge pull request #211 from gvwilson/master

Blog post about teaching commercially.
Pulling the latest updates to the 3_0 and 4_0 lessons.