fix for epubcheck reports and temporary fix for HTM-047 viewport issue

 * deleting HTM-047 errors (see #111)
 * prettier epubcheck HTML reports (as well as more in line with validator.idpf.org)
 * sorted epub:type/class/element usage statistics
 * fixed parsing of epubcheck XML reports
Merge pull request #117 from nlbdev/issue-111-tempfix

fix for epubcheck reports and temporary fix for HTM-047 viewport issue