Introduces ordering for pitstops

Pitstops are now ordered by ascending odometer value instead of
their id

app/entities.py

@@ -73,7 +73,8 @@ class Vehicle(db.Model):
     owner_id = db.Column(db.Integer, db.ForeignKey('user.id'))
     name = db.Column(db.String(255))
     pitstops = db.relationship(
-        'Pitstop'
+        'Pitstop',
+        order_by="asc(Pitstop.odometer)"
     )
     services = db.relationship(
         'Service'