Refactor duplicate Data Transfer Object

[iluwatar]

In #1570 enum based Data Transfer Object was merged. However, it brought some problems:

• It has been created in its own folder like a new pattern although we already have data-transfer-object. Due to that it's duplicating information in many places including README.md and can't be differentiated on the web site
• I'm not sure the test coverage is sufficient. This one only has AppTest.java
• It's not using local variable type inference (var)

Let's refactor it into the same data-transfer-object folder as an alternative implementation and address the lack of tests and missing vars.