en-GB.plg_content_hyarticle.ini ver 3.1.1.0

- Modify PLG_CONTENT_HYARTICLE_XML_DESCRIPTION
- Added strings for the following
-- Label & Desc strings for title css classes field
-- Label & Desc strings for intro image css classes field
-- Label & Desc strings for fulltext image css classes field
-- Label & Desc strings for image caption css classes field