Added exceptions for the subtitle and video types in .gitignore
Fixed small type issue
[dailymotion] Added support for subtitles + new InfoExtractor for
generic subtitle download.

The idea is that all subtitle downloaders must descend from SubtitlesIE
and implement only three basic methods to achieve the complete subtitle
download functionality. This will allow to reduce the code in YoutubeIE
once it is rewritten.
Undo the previous commit (it was a mistake)
[internal] Improved subtitle architecture + (update in
youtube/dailymotion)

The structure of subtitles was refined, you only need to implement one
method that returns a dictionnary of the available subtitles (lang, url) to
support all the subtitle options in a website. I updated the subtitle
downloaders for youtube/dailymotion to show how it works.
Separated subtitle options in their own group
[subtitles] removed only-sub option (--skip-download achieves the same
functionality)
[test] Cleaned subtitles tests
[subtitles] Improved docs + new class for servers who don't support
auto-caption
[subtitles] Skips now the subtitles that has already been downloaded.

Just a validation for file exists, I also removed a method that wasn't
been used because it was a copy paste from FileDownloader.
[subtitles] Added tests to check correct behavior when no subtitles are
available
Merge branch 'master' into subtitles_rework
Merge branch 'master' into subtitles_rework
Merge branch 'master' into subtitles_rework
[subtitles] fixed multiple subtitles language separated by comma after merge

As mentioned in the pull request, I forgot to include this changes.
https://github.com/rg3/youtube-dl/commit/aa6a10c44a8e2e86f709c5301f9ea6ac3f01f002
Merge branch 'master' into subtitles_rework
Merge branch 'master' into subtitles_rework
[subtitles] made inheritance hierarchy flat as requested
[youtube] move subtitles methods from the base extractor to YoutubeIE
[subtitles] rename SubitlesIE to SubtitlesInfoExtractor

Otherwise it can be automatically detected as a IE ready for use.