Add location of last selected stability point structures file: - Introduced the StructureCollection for the StabilityPointStructuresFailureMechanism to ensure unique structures based on their IDs and to store the file location from were they were imported -- Updated affected files and tests - Updated migration script and test: IDs need to be unique Related to Issue [WTI-1183] git-svn-id: https://repos.deltares.nl/repos/WettelijkToetsInstrumentarium/trunk@9929 5a3db67b-de53-47b5-99c8-a1c30a6650e2