Bep 863 updater

Implementes variant handling for the record(Insert|Update|Delete) methods.

### Database changes

Contains database changes. Stayed with the old numbering scheme in here, since developers might depend on this. Even the new scheme works with DBDeploy, this does not mean it will work with every plugin…

### Possible BC breaks

Also changes some interfaces in a way, which should be mostly backwards compatible regarding old implementations. (eg. strings from older implementations are converted into objects properly (ProductId))

Changes the interface of the Gateways, since we must pass the groupId in some locations. Even as an optional Parameter this would break existing implementations. Since most use our Gateway implementations anyways, I use non-optional parameters here.

### Tests

There are some new feature tests for the variant handling.

The intershop-handling is not explicitely tested, but we assume this works. It should be verified especially for communication between "old" and "new" shop SDKs.