EZP-21191: split ezxhtml5 schema into input and output schemas
EZP-21191: introduced XmlBase
EZP-21191: split xhtml stylesheets into input and output stylesheets
EZP-21191: extract custom schema and define block and inline extension points
EZP-21191: split xhtml fragment and docbook stylesheets
EZP-21191: simplify imported schema location path
EZP-21191: refactor custom tag stylesheets
EZP-21191: update configuration