Feature to increasingly narrow tags in tag view

[digitalsignalperson]

Building off https://github.com/akissinger/dodo/pull/30 to work with complex tags, I added the ability to filter the tag view with increasing narrowing.

• allow narrowing to tags
  • N = new panel with narrowing to the current selected tag
  • n = refresh current panel (and update title) with narrowing to the selected tag, or open search if can't be narrowed further
  • b = undo last narrowing in current panel
  • space = open search view without including current selected row
• show tag view info in help panel
• in search view don't show tags that are in queries with multiple tags

For each sequential narrowing, the tag query gets another AND, so you can drill down into complex tag queries.