Let .navbar-wrapper flow in Carousel example

A .navbar-wrapper followed by a .carousel works well in this example,
but when the navbar is not followed by a carousel, content flows
underneath the navbar because it is absolutely positioned.

Letting .navbar-wrapper be part of the flow and moving the negative
margin to the .carousel to bring it underneath the navbar makes these
example styles suitable for pages without carousels.
Merge pull request #2 from ssorallen/master

Let .navbar-wrapper flow in Carousel example