remove raven/sentry fro pip-requirements; add celery in version 3.1.5
remove raven/sentry fro pip-requirements; add celery in version 3.1.5

amcat/amcat,tschmorleiz/amcat,tschmorleiz/amcat,tschmorleiz/amcat,amcat/amcat,amcat/amcat,amcat/amcat,amcat/amcat,tschmorleiz/amcat,amcat/amcat,tschmorleiz/amcat