Some refinements on bib heading jump links

journal titles don't typeset well in a little grid, so force them to
take up a full row. And italicize.

also, ensure bib sections have reasonable ids (view.bib.id) so that
journal titles with spaces in them don't break the jump links.
regenerate minified source
helper text on bib nav
first draft of issue sorting / display
more generic bib_headings approach

store the possible major/minor sort keys in a global, VIS.bib_keys.
We'll validate sort choices against this global. We'll also use it to
set a CSS class on each bib heading, so that we can style different
major keys differently (not a beautiful solution, but lets us flow long
sort headings differently).
more bib heading styling

and set a max height on the bib headings list, so that it has a scroll
bar rather than spilling off the screen when it gets too tall
regenerate minified source
Merge branch 'master' into gh-pages