Global import optimize.

This is the result of running 'Optimize imports' on the entire project.
Unfortunately it appears that while checkstyle _requires_ an empty line between
import groups, it doesn't care if there extraneous empty lines.
I double-checked our checkstyle config against docs, and don't see anything we
can tune here.

Testing Done:
./gradlew build

Reviewed at https://reviews.apache.org/r/16576/
Releasing aurora-0.3.0
Bumping up snapshot version to 0.4.0
Adding initial image in images directory
Doc images
User doc overview
Client commands doc
Tutorial doc
Configuration file reference
User guide doc
Configuration tutorial
Resource isolation doc
Client command hooks doc