Refactoring, see below description for detail

- Remove AggregateRoot because it doesn't bring much goodness as expected
- Remove non-generic version of IRepository because it's not used at the moment, so we remove it to keep the core clean
- Remove SaveChanges in ICommerceDatabase, because the IRepository is not a unit of work now,
  each call to Insert/Delete will touch the database, so the SaveChanges will be confusing
Merge branch 'master' of https://github.com/Kooboo/Ecommerce
Move init-data.sql to database folder