New Stylesheets for processing track changes to TEI to/from oXygen Author mode and other editing formats

[ebeshero]

This is related to #677 re translating track changes markup from various document editing contexts to TEI <add> and <del>. What new stylesheets can we prepare for editing oXygen XML Author mode documents, and other document formats with track-changes features beyond Word?

This is relevant to the new SIG on Computable Text and Media.