Navbar refactor

* Now responsive by default (fits better with mobile-first approach)
* Requires `.nav-header` to group `.navbar-brand` and `.navbar-toggle`
for proper mobile display.
* Changed `.nav-collapse` to `.navbar-collapse`
* Simplified examples in docs
Merge branch '3.0.0-wip' into bs3_navbar_overhaul

Conflicts:
	components.html
	dist/css/bootstrap.min.css
invert dropdown styles in navbar for inverse variation
fix mixin code example
Merge pull request #9427 from saiwang/fix-example-snippet

fix mixin code example
fixes #9431: specify font-size in dropdown menus to avoid inheritance issues
Merge branch '3.0.0-wip' of github.com:twbs/bootstrap into 3.0.0-wip
lighter default navbar, add borders to navbars, tweak padding and alignments
Merge branch '3.0.0-wip' into bs3_navbar_overhaul

Conflicts:
	dist/css/bootstrap.min.css
Merge pull request #9403 from twbs/bs3_navbar_overhaul

BS3: Navbar overhaul
fix navbar border in docs
fix up broken tests by removing empty attr
better rc2 download action
Swapped input-lg and input-sm

Fixing my own error. Thanks to @kyleledbetter for reporting.
Merge pull request #9437 from ggam/patch-1

Swapped input-lg and input-sm
nuke the box-shadow on uncollapsed navbar-collapse
only affix the sidenav in the docs if the viewport is >800px tall (fixes #8704 and avoids #8721)
Merge branch '3.0.0-wip' of github.com:twbs/bootstrap into 3.0.0-wip
grunt dist on prev forms change