Create a checkbox component

[lancewillett]

Raised by @johnHackworth

Right now, most of the checkboxes in the platform are just regular <input type="checkboxes">, styled to use a noticon on their :before psedoselector to change how they look when checked.

We should create a new react component that encapsulates the functionality and use Gridicon for it, avoiding CSS hacks to customize the look.

It's worth noting that we already have https://github.com/Automattic/wp-calypso/tree/master/client/components/forms/form-checkbox . Maybe it would be better to just rename that component (since it's not doing anything form-related, it could become client/components/checkbox ) and work from it. And if in the future we need any checkbox with a form-related behavior, add a new from-checkbox component again.

[lancewillett]

See #5323 for updated effort. Closing this ticket as the work is tracked in the pull request.