OZG-2966 OZG-3171 add usermanager related links only if configured

...y-server/src/main/java/de/itvsh/goofy/RootController.java

...vsh/goofy/common/LinkedUserProfileResourceSerializer.java

...ver/src/main/java/de/itvsh/goofy/common/ModelBuilder.java

...in/java/de/itvsh/goofy/common/UserProfileUrlProvider.java

...ava/de/itvsh/goofy/common/user/UserManagerProperties.java

...va/de/itvsh/goofy/common/user/UserManagerUrlProvider.java

...in/java/de/itvsh/goofy/common/user/UserRemoteService.java

.../java/de/itvsh/goofy/historie/HistorieModelAssembler.java

...a/de/itvsh/goofy/postfach/PostfachMailModelAssembler.java

...rver/src/test/java/de/itvsh/goofy/RootControllerTest.java

...src/test/java/de/itvsh/goofy/common/ModelBuilderTest.java

...ava/de/itvsh/goofy/common/user/UserRemoteServiceTest.java

...a/de/itvsh/goofy/historie/HistorieModelAssemblerTest.java

.../itvsh/goofy/postfach/PostfachMailModelAssemblerTest.java

.../java/de/itvsh/goofy/vorgang/VorgangControllerITCase.java