Added DAO implementation, modified readme, and added UML diagram

dao/src/main/java/com/iluwatar/App.java

@@ -0,0 +1,47 @@
+package com.iluwatar;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 
+ * With the DAO pattern, we can use various method calls to retrieve/add/delete/update data without directly
+ * interacting with the data directly. The below example demonstrates basic operations: select, add, update, and delete.
+ */
+public class App {
+
+	public static void main(String[] args) {
+
+		CustomerDaoImpl customerDao = new CustomerDaoImpl(generateSampleCustomers());
+
+		System.out.println("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
+		System.out.println("customerDao.getCusterById(2): " + customerDao.getCusterById(2));
+
+		Customer customer = new Customer(4, "Dan", "Danson");
+		customerDao.addCustomer(customer);
+
+		System.out.println("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
+
+		customer.setFirstName("Daniel");
+		customer.setLastName("Danielson");
+		customerDao.updateCustomer(customer);
+
+		System.out.println("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
+
+		customerDao.deleteCustomer(customer);
+
+		System.out.println("customerDao.getAllCustomers(): " + customerDao.getAllCustomers());
+	}
+
+	public static List<Customer> generateSampleCustomers() {
+		Customer customer1 = new Customer(1, "Adam", "Adamson");
+		Customer customer2 = new Customer(2, "Bob", "Bobson");
+		Customer customer3 = new Customer(3, "Carl", "Carlson");
+
+		List<Customer> customers = new ArrayList<Customer>();
+		customers.add(customer1);
+		customers.add(customer2);
+		customers.add(customer3);
+		return customers;
+	}
+}