Refactor API Schema and validation

- /schema now returns full openapi/swagger schema
- That schema is used to validate incoming requests
- And used as a contract in future integration tests
- Moved route files up one level
- Fixed incorrect 404 reponses when getting objects
- Fixed saving new objects and passing jsonschemavalidation

backend/schema/components/user-list.json

@@ -0,0 +1,7 @@
+{
+	"type": "array",
+	"description": "User list",
+	"items": {
+		"$ref": "./user-object.json"
+	}
+}