refactor: migrations structure

fix: cascade for alias user foreign key constraint

migrations/fixtures/1_imprint_content.sql

@@ -0,0 +1,8 @@
+-- +migrate Up
+-- SQL in section 'Up' is executed when this migration is applied
+insert into key_string_values ("key", "value") values ('imprint', 'no content here');
+
+-- +migrate Down
+-- SQL section 'Down' is executed when this migration is rolled back
+SET SQL_MODE=ANSI_QUOTES;
+delete from key_string_values where key = 'imprint';