Add key serializer, API endpoints and API tests to the django_gpg app.

mayan/apps/django_gpg/serializers.py

@@ -0,0 +1,17 @@
+from __future__ import unicode_literals
+
+from rest_framework import serializers
+
+from .models import Key
+
+
+class KeySerializer(serializers.ModelSerializer):
+    class Meta:
+        extra_kwargs = {
+            'url': {'view_name': 'rest_api:key-detail'},
+        }
+        fields = (
+            'algorithm', 'creation_date', 'expiration_date', 'fingerprint',
+            'id', 'key_data', 'key_type', 'length', 'url', 'user_id'
+        )
+        model = Key