Optimized backlog searches for torrentleech and TvTorrents providers

(Ref. my last comment in Pull Request #107)

- In the "_get_season_search_strings" methods I have removed code which
  adds episode specific search strings if not all episodes in the
  season are wanted. This is an optimization to remove unnecessary
  searches as the season search strings (i.e. "ShowName S01) should
  catch all episodes in that season anyway. I recommend doing the same
  with the other torrent providers, and in the case that they have too
  low a number of results per page instead add support for iterating the
  result pages.
- I suspect the reason all torrent providers do not add the actual season
  search string and use episode specific search strings instead, is to
  avoid downloading a season torrent when not all episodes are wanted.
  To still avoid this from happening I have instead disabled the code
  in "search.py" that picks up the season torrent if not all episodes
  in the season are wanted (which was not used anyway).