Pass correct box URL to tools when boxes live on different servers

Previously boxes on different servers haven't been able to talk to each other, because `tool/content.coffee` has assumed a dataset and its views must always be on the same server.

This has affected a number of our users who have upgraded, then created new views on their datasets, which are all mysteriously broken because they're trying to call the wrong server.

It would be good to have this deployed as soon as possible.