TextEditorView now has a set of utility functions for binding various

things in a consistent way.
bindRichTextAttr() will cause the TextEditorView's richText flag to

be initially set and bound to an attribute on a model. It will not save

out to that attribute, as in practice that's not very useful to us (we

tend to pull data out of the editor when we go to save).
Passing bindRichText: {model: ..., attrName: ...} to the constructor

will initiate a bindRichTextAttr() automatically.
bindRichTextCheckbox() will bind the richText flag to a checkbox,

synchronizing state both ways. This is used internally for the

inlineEditor, but will also be used in other locations.
bindRichTextVisibility() will bind the richText flag to the

visibility of an element. This is also used internally for the Markdown

Reference link, and will be used elsewhere.
Unit tests have been added to cover these cases.

Unit tests pass.
Tested manually with different settings, along with some upcoming changes.