allow content in titlepage, fixed usage of author and title

doctitle and docauthor was already created in DTBook based on the OPF metadata from EPUB. However, there were inconsistencies to this rule, which should now be fixed.


# epub validation

 * allow content in titlepage, fixes #191
   * titlepage is validated like any other frontmatter, except that its h1 needs to have epub:type="fulltitle" and class="title". The conversion logic does not need these attributes anymore, but it's required by the guidelines, and it makes for good semantic markup and easy css styling anyway. added these rules to check that markup is according to guidelines:
     * `[nordic263] the titlepage must have a headline (and the headline must have epub:type="fulltitle" and class="title")`
     * `[nordic264] the headline on the titlepage must have a epub:type with the value "fulltitle"`
     * `[nordic264] the headline on the titlepage must have a class with the value "title"`
 * allow the use of epub:type="fulltitle" anywhere in content
 * allow the use of epub:type="z3998:author" everywhere where the `<author>` element would be allowed in DTBook. These rules are removed:
   * `[tpb135b] z3998:author is only allowed either in the titlepage or inside a poem`
   * `[nordic262] Only <h1 epub:type="fulltitle" class="title"> and <p epub:type="z3998:author" class="docauthor"> are allowed on the titlepage.`
 * renamed tpb135a into nordic135 and updated it to work with the way poems are marked up in guidelines revision 2015-1


# dtbook-to-epub3

 * made sure jacketcopy and endnote is properly mapped to cover and rearnote even when not running in legacy mode
 * convert `<author>` inside `<level1 class="titlepage">` into `<p epub:type="z3998:author" class="docauthor">` (won't ever happen though; `<author>` is not allowed in this context)
 * convert `<h1>` inside `<level1 class="titlepage">` into `<h1 epub:type="fulltitle" class="title">`
 * added/updated XSLT unit tests for the changes


# epub3-to-dtbook

 * fixed mapping of poem title
 * fixed mapping of poem author
 * fixed mapping of poem
 * added/updated XSLT unit tests for the changes