Spring-boot: Improve the package structure documented in the "Structuring your code" section

[ShawnTuatara]

https://github.com/spring-projects/spring-boot/blob/master/spring-boot-docs/src/main/asciidoc/using-spring-boot.adoc#structuring-your-code

I was wanting to share examples of good package structure based on feature and not by service layer. This was inspired by Mike Gehard's presentation around moving from a monolith to microservices (Step 2 - https://youtu.be/Tx5h3hdvjfw?t=15m33s). I am thinking it would be good to show the same type of structure within the Spring Boot docs to inform developers of that type of structure.

Another reference for this was the java practices page: http://www.javapractices.com/topic/TopicAction.do?Id=205

[philwebb]

Changing the "Here is a typical layout" tree would probably be a nice idea.

[renjithgr]

Replaced the existing sample with this one.

com
 +- example
     +- myApplication
         +- Application.java
         |
         +- customer
         |   +- Customer.java
         |   +- CustomerController.java
         |   +- CustomerService.java
     |   +- CustomerRepository.java
         |
         +- order
     |   +- Order.java
         |   +- OrderController.java
     |   +- OrderService.java

| +- OrderRepository.java

[wilkinsona]

Duplicate of #9907