This patch adds support for using LAST as qualifier and source value. In addition, the foreground mode should work correctly by now.

Implementation Remarks: $last_item always points to the item most recently created. It remains empty as long as no new item gets created.

Example:

CREATE
LAST	Len	"Example"
Q10	P20	Q30	P40	LAST
Q10	P50	Q60	S40	LAST

The feature was tested on test.wikidata.org in background mode.