Generate the list of IEs automatically

It seems like GenericIE needs to be last, but other than that, the order really does not matter anymore.
To cut down on merge conflicts, generate the list of IEs automatically.

youtube_dl/extractor/__init__.py

@@ -64,84 +64,18 @@
 from .youtube import YoutubeIE, YoutubePlaylistIE, YoutubeSearchIE, YoutubeUserIE, YoutubeChannelIE
 from .zdf import ZDFIE
 
+_ALL_CLASSES = [
+    klass
+    for name, klass in globals().items()
+    if name.endswith('IE') and name != 'GenericIE'
+]
+_ALL_CLASSES.append(GenericIE)
 
 def gen_extractors():
     """ Return a list of an instance of every supported extractor.
     The order does matter; the first extractor matched is the one handling the URL.
     """
-    return [
-        YoutubePlaylistIE(),
-        YoutubeChannelIE(),
-        YoutubeUserIE(),
-        YoutubeSearchIE(),
-        YoutubeIE(),
-        MetacafeIE(),
-        DailymotionIE(),
-        GoogleSearchIE(),
-        PhotobucketIE(),
-        YahooIE(),
-        YahooSearchIE(),
-        DepositFilesIE(),
-        FacebookIE(),
-        BlipTVIE(),
-        BlipTVUserIE(),
-        VimeoIE(),
-        MyVideoIE(),
-        ComedyCentralIE(),
-        EscapistIE(),
-        CollegeHumorIE(),
-        XVideosIE(),
-        SoundcloudSetIE(),
-        SoundcloudIE(),
-        InfoQIE(),
-        MixcloudIE(),
-        StanfordOpenClassroomIE(),
-        MTVIE(),
-        YoukuIE(),
-        XNXXIE(),
-        YouJizzIE(),
-        PornotubeIE(),
-        YouPornIE(),
-        GooglePlusIE(),
-        ArteTvIE(),
-        NBAIE(),
-        WorldStarHipHopIE(),
-        JustinTVIE(),
-        FunnyOrDieIE(),
-        SteamIE(),
-        UstreamIE(),
-        RBMARadioIE(),
-        EightTracksIE(),
-        KeekIE(),
-        TEDIE(),
-        MySpassIE(),
-        SpiegelIE(),
-        LiveLeakIE(),
-        ARDIE(),
-        ZDFIE(),
-        TumblrIE(),
-        BandcampIE(),
-        RedTubeIE(),
-        InaIE(),
-        HowcastIE(),
-        VineIE(),
-        FlickrIE(),
-        TeamcocoIE(),
-        XHamsterIE(),
-        HypemIE(),
-        Vbox7IE(),
-        GametrailersIE(),
-        StatigramIE(),
-        BreakIE(),
-        VevoIE(),
-        JukeboxIE(),
-        TudouIE(),
-        CSpanIE(),
-        WimpIE(),
-        HotNewHipHopIE(),
-        AUEngineIE(),
-        GenericIE()
-    ]
+    return [klass() for klass in _ALL_CLASSES]
 
 def get_info_extractor(ie_name):
     """Returns the info extractor class with the given ie_name"""