Flow exporting/importing (#187)

* stages/*: Add SerializerModel as base model, implement serializer property

* flows: add initial flow exporter and importer

* policies/*: implement .serializer for all policies

* root: fix missing dacite requirement

passbook/policies/dummy/models.py

@@ -6,6 +6,7 @@ from typing import Type
 from django.db import models
 from django.forms import ModelForm
 from django.utils.translation import gettext_lazy as _
+from rest_framework.serializers import BaseSerializer
 from structlog import get_logger
 
 from passbook.policies.models import Policy
@@ -24,6 +25,12 @@ class DummyPolicy(Policy):
     wait_min = models.IntegerField(default=5)
     wait_max = models.IntegerField(default=30)
 
+    @property
+    def serializer(self) -> BaseSerializer:
+        from passbook.policies.dummy.api import DummyPolicySerializer
+
+        return DummyPolicySerializer
+
     def form(self) -> Type[ModelForm]:
         from passbook.policies.dummy.forms import DummyPolicyForm