DataRowDiff + test - unused imports cleanup
DataTableDiff: rm table1 attrib, rm listener c-tor
 - table attribute removed to better align with current 2-arg diff convention
 - passing listener via c-tor is not so helpful: inherited addListener should be
   good enough
Add MatchingMaskBuilder
Extract buildMatchingMask to separate class
Refactor DataTableDiff: use MatchingMaskBuilder