Downloader and renamer improvements

This PR contains the following features / improvements:
- When using black hole, pneumatic or sinology downloaders, their snatched releases are not ignored anymore when a another downloader that does support the check_snatched functionality is used in parallel
- All movie is renamed to media in the renamer
- Only downloaders that actually have snatched releases are polled and supplied with the ids CPS is interested in. So far, however, I couldn't find any downloader API that supports this type of status query instead of getting the full queue  :(
- Don't remove historic data when doing a full scan. - Fixes #2572
- Don't tag .ignore files - Fixes #2362 and #2557 partially (rest is already fixed in develop)
- Extend os.path.sep to all folder checks - Expands 50c5044
- Check for releases with a download_id but without download_downloader (legacy issue) - Fixes #2539
- Convert windows path to *nix path in sp - Fixes #2594

I have checked all functionality and it is ready to be pulled.