* REFACTOR: use functions from ddl-help
* NEW: Default values are written to DDL
* fix testcase for sqlserver as default constraints will get names in future
* Reading DbMigration
* ADD: DbmIgrationGenerateTest
* Tables must be created first
* Sanity checks and some getters
* DdlMigration gets applied now
* ADD: Testcase and reference migration scripts
* no effective code changes: add comments
