DOC: Filter site registry from definitions-app

For details, see CFGUI-140

• Filter site registry from definitions-app
  (https://git.magnolia-cms.com/users/rdhar/repos/definitions-app/commits/9af62e929264eae7b2b544a3a40913e267a7c936)
  • Module registry already displays the entire site/multsite definition when they are decorated 
  • Site registry cannot display decorations coming from file sources correctly
• Add support to render HTML in value column
  (https://git.magnolia-cms.com/users/rdhar/repos/definitions-app/commits/4e984f73e672a9c0fc383401ad0ed13bc0b55bce)