Write first draft of the RecipeRegister class

src/main/java/no/ntnu/idatt1002/demo/data/recipes/RecipeRegister.java

+package no.ntnu.idatt1002.demo.data.recipes;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class RecipeRegister {
+
+    private List<Recipe> recipes = new ArrayList<>();
+
+
+    //TODO: Copy-constructor
+
+    public void addRecipe (Recipe recipe) {
+        if(recipes.contains(recipe)) {
+            throw new IllegalArgumentException("The recipe already exists in the register."); // Or just replace?
+        } else if (recipe == null) {
+            throw new IllegalArgumentException("The recipe cannot be null.");
+        }
+        this.recipes.add(recipe);
+
+    }
+}