Revert "Remove unused lsnr management from Diff api"

This reverts commit 02549eaeede58731391001d692abce73455bb722.
rm clearLesteners from Diff
rm unused c-tor DiffBase(DiffListener...)
refactor CompositeDiff: childDiff as member
DataRowDiffTest: test child diff calls via mock
DataRowDiffTest: static import of captor factory method
DataRowDiffTest: add test for exception processing
DataRowDiffTest: helper verification of results
Add diff(MatchResult) to DiffBase
That also allowed testing exception handling in DataRow
Move common obj1, obj2, result to DiffBase.DiffRunner