Added GetZAtL routine for RingtoetsPipingSurfaceLine. Moved Math2D from Piping.IO to Piping.Data to prevent cyclic dependency. Related to Issue [WTI-29]git-svn-id: https://repos.deltares.nl/repos/WettelijkToetsInstrumentarium/trunk@739 5a3db67b-de53-47b5-99c8-a1c30a6650e2Former-commit-id: 83fdd9831a6aac3bbd5a95fe8449df475a9ad94c