This PR adds the TEI Stylesheets as git-submodule and updates them to 7.56.0
moreover, it
add a new directory add/data/xslt/tei where the TEI Stylesheets live in the Stylesheets folder
moves the corresponding XSLTs for transforming TEI body and TEI header to HTML to new locations add/data/xslt/tei/profiles/edirom-body and edirom-header respectively
reworks the body and header XSLTs (as far as test data and setup permitted) to work with the new version of the TEI Stylesheets
add/data/xslt/teiwhere the TEI Stylesheets live in theStylesheetsfolderadd/data/xslt/tei/profiles/edirom-bodyandedirom-headerrespectively