add button to toggle the optional theme when viewing the docs; fixes #9764
regenerate minified docs JS & CSS
Merge branch 'master' into docs-theme-toggler

Conflicts:
	docs/assets/css/docs.min.css
move it to the sidebar
Merge branch 'master' into docs-theme-toggler

Conflicts:
	dist/css/bootstrap.css.map
	dist/css/bootstrap.min.css
	docs/assets/css/docs.min.css
	docs/dist/css/bootstrap.css.map
	docs/dist/css/bootstrap.min.css
Merge pull request #13463 from twbs/docs-theme-toggler

add button to toggle the optional theme when viewing the docs