Adding default roles works

.../entities/src/main/java/at/tuwien/entities/user/Role.java

...es/src/main/java/at/tuwien/entities/user/RoleMapping.java

...src/main/java/at/tuwien/entities/user/RoleMappingKey.java

.../entities/src/main/java/at/tuwien/entities/user/User.java

fda-ui/api/user/index.js

...ervice/src/main/java/at/tuwien/endpoint/UserEndpoint.java

.../main/java/at/tuwien/exception/RoleNotFoundException.java

.../java/at/tuwien/repository/jpa/RoleMappingRepository.java

...rc/main/java/at/tuwien/repository/jpa/RoleRepository.java

...services/src/main/java/at/tuwien/service/RoleService.java

...services/src/main/java/at/tuwien/service/UserService.java

...src/main/java/at/tuwien/service/impl/RoleServiceImpl.java

...src/main/java/at/tuwien/service/impl/UserServiceImpl.java