Added Simple Navbar

We used the `navbar` class to style some links on the top of the page.
We have ONLY applied styling.
On wide screens, the links will appear horizontally, and on narrow ones
they will stack.
Added Toggle to Navbar

Added Button with classic triple bar symbol.

Utilized collapse plugin and invoked with Data-Toggle Syntax
http://getbootstrap.com/javascript/#collapse

Added `collapse` class to the links to set the initial state as
collapsed.