Downbit 0.2.7

• A download whose streams need FFmpeg to merge gets FFmpeg then, and
  merges them, rather than failing once they're downloaded. Formats that
  only FFmpeg merges, as WebM, get it before they download.
• A quality chosen in the preview survives a retry. When the site lists
  other formats on the next look, as YouTube may, the download takes the
  best there is up to that quality, rather than failing with "no format".
• The library chooses several downloads at once: ticks on the pictures,
  Cmd- and Shift-clicks, the arrows, Cmd+A, or a sweep from between the
  tiles. A bar over the list pauses, resumes, retries, reveals, copies the
  links of, removes or trashes them together, and a drag carries all
  their files. Removing has an Undo.