Add read-only style for attributes within entities in annotator

[bctcvai]

While permissions could be used to manage read-only behavior at the datum level -- specifically if the UI recognized certain elements from certain versions as read-only that may be a heavy weight solution to prevent edits of data that shouldn't be 'easy' to change.

Previous attempts of this included setting the mark of an object to -1, which the UI honors to make all attributes of that object read-only. This worked well for attachment-based data and impacted the whole datum.

Adding a 'read-only' capability to style of AttributeType would allow for partial read-only within the same datum; at least from the UI perspective which generally answers the mail for many cases.