added category service

src/main/java/ntnu/idatt2016/v233/SmartMat/service/product/CategoryService.java

+package ntnu.idatt2016.v233.SmartMat.service.product;
+
+import lombok.AllArgsConstructor;
+import ntnu.idatt2016.v233.SmartMat.entity.product.Category;
+import ntnu.idatt2016.v233.SmartMat.repository.product.CategoryRepository;
+import org.springframework.stereotype.Service;
+
+import java.util.Optional;
+
+/**
+ * Service for Categories
+ * @version 1.0
+ * @Author Birk
+ * @since 26.04.2020
+ */
+@Service
+@AllArgsConstructor
+public class CategoryService {
+
+    CategoryRepository categoryRepository;
+
+    /**
+     * gets a category
+     * @param name The name of the category
+     * @return An optional containing the category if it exists
+     */
+    public Optional<Category> getCategoryByName(String name) {
+        return categoryRepository.findById(name);
+    }
+}