* Scope .form-check-input layout to the .form-check parent

* Remove margin-bottom from list-group-items in case they are label elements

* document .form-check in input groups and list groups, and cleanup the no-label examples in the main .form-check docs

This section is meaningless and doesn't serve any purpose.

Without this, coveralls didn't receive the branch info thus leading to failures when we switched branches.

* Remove outline from select box in FF

* Use $form-select-color

Stack in cards in one column when < md

Now there's only one command needed to run the docs: `npm run docs-serve`.

Also, simplify the npm scripts.

See https://github.com/twbs/bootstrap/pull/29368#issuecomment-528725686