Rename LookupRef.id to uri, and add an id field
LookupRef.id is now LookupRef.uri
Some references to LookupRef.id() were not updated to use LookupRef.uri()
Serialise and deserialise opaque IDs on LookupRefs
Consolidate LookupRef translation into its own translator
Merge pull request #78 from atlasapi/add-ids-to-lookup-refs

Add ids to lookup refs