Implement Interfaces for services. CLoses #5.

pet-clinic-data/src/main/java/sk/jusska/sfgpetclinic/service/OwnerService.java

+package sk.jusska.sfgpetclinic.service;
+
+import java.util.Set;
+import sk.jusska.sfgpetclinic.model.Owner;
+
+public interface OwnerService {
+
+    Owner findByLastName(String lastName);
+
+    Owner findById(Long id);
+
+    Owner save(Owner owner);
+
+    Set<Owner> findAll();
+}

pet-clinic-data/src/main/java/sk/jusska/sfgpetclinic/service/PetService.java

+package sk.jusska.sfgpetclinic.service;
+
+import java.util.Set;
+import sk.jusska.sfgpetclinic.model.Pet;
+
+public interface PetService {
+
+    Pet findById(Long id);
+
+    Pet save(Pet owner);
+
+    Set<Pet> findAll();
+}

pet-clinic-data/src/main/java/sk/jusska/sfgpetclinic/service/VetService.java

+package sk.jusska.sfgpetclinic.service;
+
+import java.util.Set;
+import sk.jusska.sfgpetclinic.model.Vet;
+
+public interface VetService {
+
+    Vet findById(Long id);
+
+    Vet save(Vet owner);
+
+    Set<Vet> findAll();
+}