Using Google Java Code Style

[dota17]

The current code format is not very good, especially when reading the code online on github. I can't stand this anymore.

I chose Google Java Code Style to reformat the source code.
The reason why I chose Google's version:

1. There is a repo for the code format profile.
2. There are 2 predefined Checkstyle configuration definitions that ship with the Maven Checkstyle Plugin, and the Google definition is the one. We can use it to help checking the code style.

I would consider adding the google checkstyle next and optimize the code format further.