Make Corpus model available in flask shell.

opaque.py

 from app import create_app, db
-from app.models import User, Role, Permission, Job
+from app.models import Corpus, User, Role, Permission, Job
 from flask_migrate import Migrate
 import os
 
@@ -10,7 +10,7 @@ migrate = Migrate(app, db)
 
 @app.shell_context_processor
 def make_shell_context():
-    return dict(db=db, User=User, Role=Role, Permission=Permission, Job=Job)
+    return dict(db=db, Corpus=Corpus, User=User, Role=Role, Permission=Permission, Job=Job)
 
 
 @app.cli.command()