Add insertText and run ember-mobiledoc-kit editor helpers

[bantic]

Usage:

// acceptance test
import { insertText, run } from '../../helpers/ember-mobiledoc-editor';

test('visit /', function(assert) {
  visit('/');
  andThen(() => {
    let editorEl = find('.mobiledoc-kit')[0];
    return insertText(editorEl, 'here is some text');
    /* Or:
      return run(editorEl, (postEditor) => ...);
    */
  });
  andThen(() => {
    // assert text inserted, etc.
  });
});

fixes #100

[bantic]

@chrisdpeters These are released in v0.5.6. Does that work for your needs in #100?

[chrisdpeters]

@bantic I switched to a bunch of API work in October, which lasted quite some time, so I was unable to try any of this out until now. I'm now messaging you 3 months into the future to say, "Thank you!"

The only problem that I've experienced so far has been with your example.

let editorEl = find('.mobiledoc-kit')[0];

With that, editorEl ends up being null.

I seem to have better luck if I use this selector: .mobiledoc-editor__editor. It looks like this class is also set on the editor element: .__mobiledoc-editor.

If you think this is indeed the correct behavior, then I could submit a small pull request with an updated README.

I'll let you know if I run across any other issues, but this seems to be working pretty well so far.

[bantic]

@chrisdpeters Thanks for the comment to let me know this is working for you! Glad that is working.
Yes, I think you are correct about using the other selector. If you are able to submit a PR for this I'd be happy to merge it. thanks!