Added option for allowing the use of high priority on recent episode downloads

- Moved detection of recent episodes from each nzb provider to "search.py"
  so its generic for both NZB and torrent providers.
- Moved priority value to the result object.
- Added option to allow high priority for recent episodes (default: true)
  to the episode search settings.
Added option to use high bandwidth allocation on high priority torrents

- Added high bandwidth allocation checkbox to torrent search settings
  (default: false)
- Option is currently only visible in the gui when using the
  transmission client.