Several multiple choice option fixes

Addresses issues mentioned in #29 (closed).

• Make migrations compatible with the migrations on master

Closes #29 (closed)

zesje/database.py

@@ -166,11 +166,9 @@ class MultipleChoiceOption(db.Model):
 
     x = Column(Integer, nullable=False)
     y = Column(Integer, nullable=False)
-    page = Column(Integer, nullable=False)
-
     label = Column(String, nullable=True)
 
-    problem_id = Column(Integer, ForeignKey('solution.id'), nullable=False)
+    problem_id = Column(Integer, ForeignKey('problem.id'), nullable=False)
     feedback_id = Column(Integer, ForeignKey('feedback_option.id'), nullable=True)