Changed SubmissionAssignmentSerializer `type_pk` to `type`

Uniform naming makes Frontend life easier

core/serializers/subscription.py

@@ -8,13 +8,13 @@ from core.serializers import (DynamicFieldsModelSerializer, FeedbackSerializer,
 
 class SubmissionAssignmentSerializer(DynamicFieldsModelSerializer):
     text = serializers.ReadOnlyField()
-    type_pk = serializers.ReadOnlyField(source='type.pk')
+    type = serializers.ReadOnlyField(source='type.pk')
     full_score = serializers.ReadOnlyField(source='type.full_score')
     tests = TestSerializer(many=True, read_only=True)
 
     class Meta:
         model = Submission
-        fields = ('pk', 'type_pk', 'text', 'full_score', 'tests')
+        fields = ('pk', 'type', 'text', 'full_score', 'tests')
 
 
 class AssignmentSerializer(DynamicFieldsModelSerializer):