Pass onChange to custom toolbar actions
Pass onChange to custom toolbar actions

Allows for much more robust (and modular) changes from custom toolbar actions. 

Example: A simple "Smile" action:

```
import { EditorState, Modifier } from 'draft-js';
import actions from 'megadraft/lib/actions/default';

export default actions.concat([
  {
    type: 'custom',
    icon: props => (
      <Smile
        {...props}
        width="24"
        height="18"
        fill="currentColor"
        fillRule="evenodd"
      />
    ),
    action(editorState, onChange) {
      const contentState = Modifier.replaceText(
        editorState.getCurrentContent(),
        editorState.getSelection(),
        '😀',
        editorState.getCurrentInlineStyle()
      );

      onChange(EditorState.push(editorState, contentState, 'insert-characters'));
    }
  }
]);
```
globocom/megadraft,globocom/megadraft,globocom/megadraft