parse HTML using parser plugins when creating editor

[bantic]

It should be possible to do:

editor = new Editor({html: 'some html...', parserPlugins: [parseNodeFn, ...]});

and have the html be parsed using the passed plugins the way that it works now when pasting in HTML.

Here's an example gist showing parsing images from HTML, e.g.

[bantic]

cc @jordpo