add ARIA roles to Dropdown examples in Components docs
add src attribute to holder.js-powered <img>s so that they validate

use `data:` URL of empty invalid PNG: src="data:image/png;base64,"
add alt text to <img>s in components.html
add alt text to <img>s in javascript.html
Components docs: Dropdowns section: add .sr-only toggle buttons so aria-labelledby validates
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' of github.com:twbs/bootstrap into 3.0.0-wip
fixes #9400: add box-sizing to pseudo elements as well
finish fixing #9295: add button group buttons to new input group sizing
Merge pull request #9396 from twbs/docs-html-validation

add HTML5 validation of docs pages to the build
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
Merge pull request #9389 from twbs/emphasize-git-HEAD

Emphasize git HEAD downloads
mention fubared state of overflow hidden on body in android and iOS to fix #8975 and #9315
Drop the accordion for the panel

* Deletes the accordion.less file
* Extends the panel to be collapsible with our JS plugin
* Supports panel color variations
copy
fix negative indenting in button group for nested button groups
fixes #8985: only specify minified dist files for bower
Added pagination-size mixin
Fixed errors