[PLAT-3937] fixed javadoc
[PLAT-3937] updated to match wiki (which fixes ids)
[PLAT-3937] fixed missing identifier
[PLAT-3937] fix for issue - ensures Portfolio objects are removed from the data source when securities are overwritten
[PLAT-3937] added validation to prevent external ids from being assigned to different trades
[PLAT-3937] added XMLLoader failure case test and test for position/trade reuse across portfolios