SMW\DISerializer add tests

++ @covers DISerializer::getSerializedQueryResult
++ @covers SMWQueryResult::toArray

Tests added in order to ensure that if the structure is altered, adoption
has been made in
- SMW\DISerialzer and
- smw.dataItem.factory()

Change-Id: Iba9946db85408d55fbbbf8bdad438d85cb3d42eb
Merge "SMW\DISerializer add tests"