fixing pitest failure by excluding purely generated code etc.

also removed unused methods and added a unit test to improve coverage
and setting thresholds now to 90% each

src/test/java/org/hostsharing/hsadminng/service/dto/MembershipDTOTest.java

@@ -0,0 +1,15 @@
+package org.hostsharing.hsadminng.service.dto;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class MembershipDTOTest {
+
+    @Test
+    public void withShouldApplyCallback() {
+        final MembershipDTO actual = new MembershipDTO().with(m -> m.setRemark("Some Remark"));
+
+        assertThat(actual.getRemark()).isEqualTo("Some Remark");
+    }
+}