Fix for coded concept broken with Most Recent Observation on dashboard TRUNK-4131

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i wouldn't use concept ids and datetime to find this obs , if the list already had some obs by the same concept and you want to get the newly created obs, a cleaner way is to find the newly included obs in the list, the commons-lang library CollectionUtils.subtract(coll1, coll2) method that which when given two collections it gives you the items in one collection that are not in the other which in this case is 1 and that should be the newly created obs, don't you think it is neater?