Page in book url

I've included quite a lot of fixes for tests, it may be easier to look at the commits instead of the complete diff.

The only relevant commit that changes from page number to page ident hash is "Use page ident hash instead of page number in url".  It fixes the legacy redirection and transformation.

I'm still working on handling `/contents/book-ident-hash:page-ident-hash` in archive.  @pumazi / @reedstrm Is it ok to just redirect to `/contents/page-ident-hash` or did we want some different custom output?