EPUB, EPUB3 templates:  Handle structured metadata on titlepage.

Previously we just expected 'title', 'subtitle', 'author', 'date'.

Now we still support those, but also support the format recommended
for epub metadata in the pandoc README:

---
title:
- type: main
  text: My Book
- type: subtitle
  text: An investigation of metadata
creator:
- role: author
  text: John Smith
- role: editor
  text: Sarah Jones
identifier:
- scheme: DOI
  text: doi:10.234234.234/33
publisher:  My Press
rights:  (c) 2007 John Smith, CC BY-NC
...
Added \VerbatimFootnotes if there is verbatim in notes.

See http://tex.stackexchange.com/questions/203/how-to-obtain-verbatim-text-in-a-footnote

Closes jgm/pandoc#1616.
Moved polyglossia/babel definitions to before biblatex; otherwise biblatex fails with xetex.
Fixed typo.
Use biblatex-chicago instead of biblatex.
Revert "Use biblatex-chicago instead of biblatex."

This reverts commit a0ea58bc2ed43a09f6c349ad20a0b1ee2791a75b.
LaTeX template:  Add shorthands=off to babel options.

This prevents special bindings of characters like " in Spanish.