More efficient citation querying

We don't ask for a cite attribute together with its section - we
extract the section and just ask for author and work then. Less to
query, less to cache.
Mild refactor in navigator
More refactor in navigator.getCitation()

Makes the function public and taking a callback, that way we can use it
elsewhere as well.
Show citation in sentence list
Merge pull request #216 from latin-language-toolkit/cite_in_list

Cite attribute handling