Added ModelMapper

Author: Somnath More

backend/src/main/java/com/reactpairdemo/demo/DemoApplication.java

@@ -1,7 +1,9 @@
 package com.reactpairdemo.demo;
 
+import org.modelmapper.ModelMapper;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.Bean;
 
 @SpringBootApplication
 public class DemoApplication {