Some bugfixes, documentation improvements minor features; some internal rework.

• add --format=json2 for mu find, which produces a bit more 'idiomatic' json
• close notifications once done
• more informative mu4e-analyze-last-query (include all parameters)
• Make mu4e-maildir-shortcut and mu4e-bookmarks understand a property
  :hide-if-no-unread, which hides the maildir/bookmark from the main-view
  if there are no unread messages which the corresponding query.