Get rid of OneJar

OneJar isn't playing nice with the AssetsBundle. Or, rather, DropWizard
isn't smart enough to go more than one level deep inside a jar, so a
jar-within-a-jar doesn't work with assets.

So, no more fat jar. Just compile into a thin jar and run with a set
classpath.
Assets!

Add some test assets, including a grumpy cat favorite icon. We'll
obviously build upon this later.