Add a plain HTML WYSWIG field

[dNitza]

We have a use case where some people can edit a post using TinyMCE. This saves HTML to a field in the database. We then have a set of users who are editing these fields with Formalist and at the moment there isn't a WYSYWIG to handle HTML fields.

It might be good to address #142 before this one so we're not adding a HTML WYSWIG component to every app that uses this lib