Removed class RimWellLogCurveImpl.
RigWellLogCurveData::calculateValidPointsIntervals() needs to be
harmonized with new way of extracting depths from well paths.
Using RigWellLogCurveData instead of RimWellLogCurveImpl. Added test
interface which has access to private methods in RigWellLogCurveData.
RimWellLogCurveImpl should probably be removed when correct filtering of
curve segments based on depths is up & running.
