It seems like uiskin.png should be placed here. Keep the one in assets/data as well since it doesn't really matter if it's there as well for now.
Added surefire-plugin to test using it  explicitly. Now supports
parallel tests.
Added checkstyle. Rules are really strict right now so easen them up if
they are too harsh.
Removed some whitespace checks. Semms unneccessary unless newline can be
added as whitespace as well. Not priority now.