fix mod preset ID not being generated

Author: fugasjunior

src/main/java/cz/forgottenempire/arma3servergui/model/ModListPreset.java

@@ -2,6 +2,7 @@
 
 import java.util.Collection;
 import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
 import javax.persistence.Id;
 import javax.persistence.OneToMany;
 import javax.validation.constraints.NotNull;
@@ -19,8 +20,8 @@
 @NoArgsConstructor
 public class ModListPreset {
 
-    @NotNull
     @Id
+    @GeneratedValue
     private Long id;
 
     @NotNull