[RichTextEditor] Allow rich text in text fields

It is sometimes necessary to style individual words or characters of a text field. Examples include

1. Underlining invalid parts of input (misspelled words with a wavy underline for instance)
2. Emphasizing something as being a recognized entity such as a key as in: "Employee *234765*".

One way of doing this would be to allow support for the <span> tag as if the document model was HTML. This would allow me to decouple the styling into a .css file. Usage example:

messageTextField.setText("Let's go out <span class="misspelled>tonght</span>");