Renamed migration script and refactor code

app/organisation/rest.py

@@ -1,14 +1,11 @@
 from flask import Blueprint, jsonify, request
 
 from app.dao.organisations_dao import (
+    dao_create_organisation,
     dao_get_organisations,
     dao_get_organisation_by_id,
-    dao_create_organisation
-)
-from app.errors import (
-    InvalidRequest,
-    register_errors
 )
+from app.errors import register_errors
 from app.models import Organisation
 from app.organisation.organisation_schema import post_organisation_schema
 from app.schema_validation import validate