implement tag and publisher logic for compiled releases

[odscjen]

Stemming from open-contracting/standard#330 -

OCDS Merge should warn if the publisher is not identical across all releases. It should accept an optional publisher argument for populating the compiled release's publisher field.

The tag array in a compiled release should accumulate all unique tag values in the individual releases that make up the compiled release as well as an additional 'compiled' tag.