Fix imports and general cleanup

· Import from compat what comes from compat. Yes, some names are available in utils too, but that's an implementation detail.
· Use _match_id consistently whenever possible
· Fix some outdated tests
· Use consistent valid URL (always match the whole protocol, no ^ at start required)
· Use modern test definitions

youtube_dl/extractor/wistia.py

@@ -1,9 +1,8 @@
 from __future__ import unicode_literals
 
-import re
-
 from .common import InfoExtractor
-from ..utils import ExtractorError, compat_urllib_request
+from ..compat import compat_urllib_request
+from ..utils import ExtractorError
 
 
 class WistiaIE(InfoExtractor):
@@ -22,8 +21,7 @@ class WistiaIE(InfoExtractor):
     }
 
     def _real_extract(self, url):
-        mobj = re.match(self._VALID_URL, url)
-        video_id = mobj.group('id')
+        video_id = self._match_id(url)
 
         request = compat_urllib_request.Request(self._API_URL.format(video_id))
         request.add_header('Referer', url)  # Some videos require this.