add arrow in picker to advertise drag-to-TOC

Tried to make the mark-up relatively nonintrusive and limit the CSS to
gh-book.
make text-shadows not over everything in the auth view
Merge pull request #65 from oerpub/58379028-picker-drag-training-wheel

add arrow in picker to advertise drag-to-TOC
Merge pull request #71 from oerpub/58566326

make text-shadows not cover everything in the auth view
update readme to include vagrant instructions
Merge remote-tracking branch 'origin/master' into 57577828
simplify adding things to opf manifest
move default opf and nav files into templates