add WingedEdge and its test
redesigned AdaptiveCellEdge and AdaptiveCell

  + add SegmentIterator
  + rename WingedEdge to AdaptiveCellEdge
  + redesigned AdaptiveCell interface
  + remove the old [Quadrangle|Triangle]AdaptiveCellTest
  + strengthen the test of AdaptiveCellEdge
  + add tests for AdaptiveCellFactorys