SeInitializer should have an addPackage(boolean, String)

For now addPackage uses Package or Class parameter. Class parameter is not great because there are packages without anything except other packages and Package is pretty strict for several use cases because it can't be created programmatically and requires a class to get an instance.

Since all implementations convert the Package instance to a String to load it, it would be very helpful to add it directly in the API IMHO.