Add @ExpectedCompositeDatabase annotation

Hi,

I have a common part of the expected XML file for each unit test. This large part depends on the database schema and it is repeated for each test. Every time I'm slightly changing the database schema, all the tests fail. This is okay, but I have to fix all the tests independently. So I decided to extract a common part into the separate file.

Unfortunately @ExpectedCompositeDatabase does not allow me to configure multiple XML files just like @DatabaseSetup. So I created a new annotation: @ExpectedCompositeDatabase. Could you please accept my pull request for this feature?