Importing (cloning) data from other domain

[joepio]

Sometimes a user wants to:

• Move data from one domain (e.g. localhost) to something else (example.com).
• Import data from another site, but clone and modify it

The current /import endpoint can probably be modified to work in these cases, too.

It can already:

• deal with local-id resources (which don't have an @id subject)

Proposal

• Add a move to current domain checkbox when importing something. When this is checked, the entire path of the resource (it's the/path in https://example.com/the/path) is interpreted as a local-id. I think this should be enabled by default, as in most cases, the user will want to change these external resources into something that can be used locally.