Use Draft-07 and Draft7Validator everywhere

We were using the Draft4Validator in one place, so this updates it to
the Draft7Validator instead.

The schemas were mostly using draft 4 of the JSON schema, though there
were a couple of schemas that were already of version 7. This updates
them all to version 7, which is the latest version fully supported by
the jsonschema Python package. There are some breaking changes in the
newer version of the schema, but I could not see anywhere would these
affect us. Some of these schemas were not valid in version 4, but are
now valid in version 7 because `"required": []` was not valid in earlier
versions.

tests/app/public_contracts/__init__.py

@@ -2,7 +2,7 @@ import os
 
 import jsonschema
 from flask import json
-from jsonschema import Draft4Validator
+from jsonschema import Draft7Validator
 
 
 def return_json_from_response(response):
@@ -22,5 +22,5 @@ def validate_v0(json_to_validate, schema_filename):
 
 
 def validate(json_to_validate, schema):
-    validator = Draft4Validator(schema)
+    validator = Draft7Validator(schema)
     validator.validate(json_to_validate, schema)

tests/app/public_contracts/schemas/v0/GET_notification_return_email.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "http://json-schema.org/draft-04/schema#",
+  "$schema": "http://json-schema.org/draft-07/schema#",
   "description": "GET notification return schema - for email notifications",
   "type" : "object",
   "properties": {

tests/app/public_contracts/schemas/v0/GET_notification_return_sms.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "http://json-schema.org/draft-04/schema#",
+  "$schema": "http://json-schema.org/draft-07/schema#",
   "description": "GET notification return schema - for sms notifications",
   "type" : "object",
   "properties": {

tests/app/public_contracts/schemas/v0/GET_notifications_return.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "http://json-schema.org/draft-04/schema#",
+  "$schema": "http://json-schema.org/draft-07/schema#",
   "description": "GET notification return schema - for sms notifications",
   "type" : "object",
   "properties": {

tests/app/public_contracts/schemas/v0/POST_notification_return_email.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "http://json-schema.org/draft-04/schema#",
+  "$schema": "http://json-schema.org/draft-07/schema#",
   "description": "POST notification return schema - for email notifications",
   "type" : "object",
   "properties": {

tests/app/public_contracts/schemas/v0/POST_notification_return_sms.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "http://json-schema.org/draft-04/schema#",
+  "$schema": "http://json-schema.org/draft-07/schema#",
   "description": "POST notification return schema - for sms notifications",
   "type" : "object",
   "properties": {

tests/app/public_contracts/schemas/v0/definitions.json

@@ -1,5 +1,5 @@
 {
-  "$schema": "http://json-schema.org/draft-04/schema#",
+  "$schema": "http://json-schema.org/draft-07/schema#",
   "description": "Common definitions - usage example: {'$ref': 'definitions.json#/uuid'} (swap quotes for double quotes)",
   "uuid": {
     "type": "string",