Uniquely identify learning resources

[pdpinch]

As a curator and as a course author, I'd like to have a way to uniquely identify learning objects that have been exported from LORE and possibly reimported again. This would help me identify and deal with duplicates, and it would also help with integrating with other systems like the ODL analytics service.

Currently we incorporate the LORE id in filenames at export. However, I don't think this will survive round-trip imports and exports from edX, and isn't conveniently machine-readable.

This might be worth a conversation with edX, as I think this is something they would like to support & may have given some thought to.