epubcheck, build info, metadata fixes, validation improvements, ++

added build info to script descriptions
added bash script for setting the build number and build time according to the git commit log
converted OPF validator from XSLT to Schematron
removed nordic:guidelines meta requirement from RelaxNG (fixed #43)
restricted nordic:* metadata check to single-document representation in Schematron
nordic2015-1.sch: fixed tpb123, tpb127, tpb128
better formatting of HTML reports
including patched version of px:fileset-store which allows for storing the xml declaration in zips
including patched version of px:unzip-fileset which allows for unzipping XML files using base64 encoding (allowing for unzipping of xml declarations)
added option "ignore-missing-images" to dtbook validator
images must always be present when converting from dtbook to epub3
epub3 validation includes epubcheck validation for generic epub3 conformance
epubs in the epub validator ar unzipped byte-for-byte (thus including their xml declaration)
epub3-validator new requires that all XML documents (XHTML, OPF, SMIL, etc) has an xml declaration
loading and storing all xhtml files as xml instead of xhtml" (avoids any serialization/parsing performed by the xproc processor)
intermediary xhtml representation now refers to images in the images directory instead of the same directory as itself; images are now instead moved during the conversion between dtbook and the intermediary xhtml instead of between the intermediary xhtml and epub3
id's are no longer explicitly set to pub-title, pub-language, pub-creator, pub-contributor and source-id for dublin core title, language, creator, contributor and source respectively (in the OPF); fixes #48
added dublin core namespace declaration to the opf
including track:Supplier in the resulting dtbook
including nordic prefix in the opf (fixes #
added xsl:message statements for meta elements that are dropped from the html metadata when converting to opf metadata
including nordic:guidelines and nordic:supplier in the opf (fixes #27, fixes #28)
added XProc tests: dtbook-to-html.convert, html-to-epub3.convert
fixed XProc tests: epub3.validate, html-to-dtbook.convert
fixed XSLT test: opf-to-html-metadata