Core: drop 2 AssociationDefinition methods (#393).

BREAKING CHANGES

2 methods are dropped from AssociationDefinition and AssociationDefinitionModel:
    - getWholeRoleTypeUri()
    - getPartRoleTypeUri()

=> Use the "dm4.core.whole" and "dm4.core.part" constants instead.

Close ticket 393.

Furthermore: "Jörn Weißenborn" is listed as a contributor in "About DeepaMehta".