fixed build bug, filenames, tests, epubcheck, etc.

* fixed build version statement; version is now read from a separate xml file and output as the first message during conversion instead of in the script description (maven filtering didn't work well with osgi service descriptor generation)
* nordic2015.sch: allow empty pages
* switched from px:fileset-store to pxi:fileset-store (allows for storing html as xml)
* added copy of patched epub3-nav-utils which contains several fixes, will revert to default version when patched version is included in the next release of dp2
* added copy of i18n-translate which will be included in the default dp2 distribution in the next official release
* added epub3 validation for unique ids across all XML files (XHTML, OPF, NCX, SMIL, etc.)
* added dc:identifier to navigation document
* fixed issue with epubcheck-report-to-pipeline-report.xsl message parsing
* content files are now named `[identifier]-[xxx]-[type].xhtml`
* chapters in parts are now properly extracted
* when joining multiple html-files, `doc[x]_` are no longer prepended to the ids, since all ids must now be unique in the first place
* added xprocspec test: html-split.split.xprocspec
* minor fix in html-to-dtbook.convert.xprocspec
* updated html-to-epub3.convert.xprocspec to have the correct filenames for the content files (`[identifier]-[xxx]-[type].xhtml`) and include the chapters which are contained in parts
* fixed duplicate id in test book
* fixed missing dtb:uid in test ncx
* added dc:identifier to xslt test: split-html.annotate.xspec
* fixed split-html.annotate.xspec to account for the chapters that are contained in parts and updated filenames