Add text boxes to workflows

It would be helpful to be able to add text boxes to workflows to contain comments from the workflow author.

As workflows get more complex, these text boxes could be used to mark a set of related steps, give more information than can fit in the label for a step, and to provide special instructions to the viewer, such as conditions that must be fulfilled before running the workflow.

The text box should be able to support different fonts, text sizes, colors, borders, etc.