* Extract color styles from .navbar { } and put them into
.navbar-default { }
* Change variable names
* Change the docs accordingly (i.e., add the .navbar-default class to
all default navbars)
* Change customizer accordingly

fixes #9790: nullify right padding in container-ed navbars when last element in collapse is a right aligned navbar nav

Addresses a few different cases where the navbar has and doesn't have a
container, and accordingly adjusts the padding and margin of key
elements.

* Defaults to no rounded corners and full width in the viewport
* When in a container, the jumbotron has extra padding and will have
rounded corners
* Updates default jumbotron example to show the full width default
display

Fixes #9759.

* Adds new "theme" example
* Adds new theme.less file to provide all the overrides and additional
styles for the theme
* theme.less compiles, via Grunt, to two new files to `dist/css`,
bootstrap-theme.css and bootstrap-theme.min.css

Make negative margins on rows the default, not just in containers, and add padding to body to compensate