grunt tasks update; fix nav-pic margin

now only copy newer files during staging and tempstage tasks
changing algorithm for determining next meal

the old algorithm had a bit of an issue when new food types were
introduced; the changes I made aren't perfect by any means, but they'll
work for now
add directive for hiding bootstrap menu on click

whenever a boostrap navbar collaspable menu is open and a link is
clicked in it, it will now close
minor changes