Fix data model before generating migration

app/database/muhscheme.txt

@@ -30,9 +30,8 @@ order_item
 
 order_item_choice
   id
+  order_item_id
   choice_id           HLDS identifier
   kind                single_choice/multi_choice
-  order_item
   name
-  description
   value               just a textual description of the chosen values

app/models/orderitemchoice.py

@@ -0,0 +1,20 @@
+from datetime import datetime
+
+from .database import db
+from .orderitem import OrderItem
+
+
+class OrderItemChoice(db.Model):
+    id = db.Column(db.Integer, primary_key=True)
+    choice_id = db.Column(db.String(64), nullable=True)
+    order_item_id = db.Column(db.Integer, db.ForeignKey("orderitem.id"), nullable=False)
+    kind = db.Column(db.String(1), nullable=False)
+    name = db.Column(db.String(120), nullable=True)
+    value = db.Column(db.String(120), nullable=True)
+
+    # pylint: disable=attribute-defined-outside-init
+    def configure(self, order: OrderItem) -> None:
+        self.order = order
+
+    def __repr__(self) -> str:
+        return "{}: {}".format(self.name, self.value)