Added NIO Selector project under core-java (#738)

* made changes to java reflection

* removed redundant method makeSound in Animal abstract class

* added project for play-framework article

* added project for regex

* changed regex project from own model to core-java

* added project for routing in play

* made changes to regex project

* refactored code for REST API with Play project

* refactored student store indexing to zero base

* added unit tests, removed bad names

* added NIO Selector project under core-java module

core-java/src/test/java/com/baeldung/java/nio/selector/EchoTest.java

@@ -0,0 +1,18 @@
+package com.baeldung.java.nio.selector;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class EchoTest {
+
+    @Test
+    public void givenClient_whenServerEchosMessage_thenCorrect() {
+        EchoClient client = EchoClient.start();
+        String resp1 = client.sendMessage("hello");
+        String resp2 = client.sendMessage("world");
+        assertEquals("hello", resp1);
+        assertEquals("world", resp2);
+    }
+
+}