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