Rename JSONModel to SerialisedModel 2/2

This class doesn’t actually wrap JSON, it wraps serialised data.

So this name feels better.

app/notifications/validators.py

@@ -21,7 +21,7 @@ from app.notifications.process_notifications import create_content_for_notificat
 from app.utils import get_public_notify_type_text
 from app.dao.service_email_reply_to_dao import dao_get_reply_to_by_id
 from app.dao.service_letter_contact_dao import dao_get_letter_contact_by_id
-from app.serialised_models import TemplateJSONModel
+from app.serialised_models import SerialisedTemplate
 
 from gds_metrics.metrics import Histogram
 
@@ -164,7 +164,7 @@ def get_template_dict(template_id, service_id):
 
 
 def get_template_model(template_id, service_id):
-    return TemplateJSONModel(get_template_dict(template_id, service_id))
+    return SerialisedTemplate(get_template_dict(template_id, service_id))
 
 
 def validate_template(template_id, personalisation, service, notification_type):

app/serialised_models.py

@@ -1,7 +1,7 @@
 from abc import ABC, abstractmethod
 
 
-class JSONModel(ABC):
+class SerialisedModel(ABC):
 
     @property
     @abstractmethod
@@ -16,7 +16,7 @@ class JSONModel(ABC):
         return super().__dir__() + list(sorted(self.ALLOWED_PROPERTIES))
 
 
-class TemplateJSONModel(JSONModel):
+class SerialisedTemplate(SerialisedModel):
     ALLOWED_PROPERTIES = {
         'archived',
         'content',