Add ListUtils for joined list

app/src/main/java/fr/iutnantes/miar/dndgenerator/api/utils/ListUtils.java

+package fr.iutnantes.miar.dndgenerator.api.utils;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * ListUtils is a class with utils methods
+ */
+public class ListUtils {
+
+    /**
+     * Method for join data inside unique list
+     * @param list Base list used for join data
+     * @param data Data used for join inside list
+     * @param <T> Class of Data
+     * @return joinedList
+     */
+    public static <T> List<T> joinList(List<T> list, T... data) {
+        return joinList(Arrays.asList(list, Arrays.asList(data)));
+    }
+
+    /**
+     * Method for join data inside unique list
+     * @param lists lists used for join data
+     * @param <T> Class of Data
+     * @return joinedList
+     */
+    public static <T> List<T> joinList(List<List<T>> lists) {
+        List<T> out = new ArrayList<>();
+        for (List<T> list: lists)
+            out.addAll(list);
+        return out;
+    }
+}

app/src/test/java/fr/iutnantes/miar/dndgenerator/api/utils/ListUtilsTest.java

+package fr.iutnantes.miar.dndgenerator.api.utils;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+
+import static fr.iutnantes.miar.dndgenerator.api.utils.ListUtils.joinList;
+import static org.junit.Assert.assertEquals;
+
+public class ListUtilsTest {
+    @Test
+    public void joinListTest() {
+        assertEquals(
+            Arrays.asList(1, 2, 3), joinList(Arrays.asList(1, 2), 3)
+        );
+        assertEquals(
+            Arrays.asList(1, 2, 3, 4),
+            joinList(Arrays.asList(Arrays.asList(1, 2), Arrays.asList(3, 4)))
+        );
+    }
+
+}