Federation: importing large amounts of distant data at once

If I import a large amount of distant resources at once (e.g. via CSV), the backlinks queue will be overrun with individual activities

This affects test scripts (#303 ), but will possibly also affect other clients too (e.g. during a database migration, Rise-for currently generates shared "representatives" data locally, but will probably want these to be imported from a distant server at some point)

Is there a way we can manage this, e.g. by changing the ActivtiyQueueService, or by sending a larger instruction to the recipient server (I don't think this is considered by the ActivityStreams standards? It may be a security problem to allow it?)