Added DefaultAssociation as a complement of DefaultAssociationRole, so we have the complete set of expected java classes.
The intend is to help to take those properties in account while working on DefaultFeature internal.


git-svn-id: https://svn.apache.org/repos/asf/sis/branches/JDK8@1593584 13f79535-47bb-0310-9956-ffa450edef68