Also delete corpus files when a corpus gets deleted

app/utils.py

@@ -63,5 +63,7 @@ def background_delete_corpus(app, corpus_id):
         logger.warning('Called by delete_thread.')
         logger.warning('Corpus id is: {}.'.format(corpus_id))
         corpus = Corpus.query.filter_by(id=corpus_id).first()
-        logger.warning('Corpus object is: {}'.format(corpus))
+        for corpus_file in corpus.files:
+            db.session.delete(corpus_file)
+            logger.warning('Corpus object is: {}'.format(corpus))
         corpus.delete_corpus()