Allow CSS classes for canonical titles, notes, and references in OSIS markup

Providing CSS classes for canonical titles, reference types, and note sub-types allows developers using the osisxhtml filter to significantly improve and customise their text presentation.

Titles with canonical="true" would convert to HTML tags having class="canonical".

References would pass any type value to their HTML tag's class attribute.

Notes would pass any subType value to their HTML tag's class attribute (because a note's type attribute is already used by the filter to create custom HTML markup).

The same approach could be applied to milestone OSIS elements by passing any type value to the class attribute of an HTML span like this: <span class="my-osis-type"></span>.