[Dumpert] Add new extractor

Add support for the Dutch video site Dumpert. http://www.dumpert.nl/

youtube_dl/extractor/__init__.py

@@ -115,6 +115,7 @@ from .drtuber import DrTuberIE
 from .drtv import DRTVIE
 from .dvtv import DVTVIE
 from .dump import DumpIE
+from .dumpert import DumpertIE
 from .defense import DefenseGouvFrIE
 from .discovery import DiscoveryIE
 from .divxstage import DivxStageIE