Update for Dropwizard 0.7-SNAPSHOT

A living PR as we wait for Dropwizard 0.7 to be released.

Tests currently pass, major changes:
* Change dropwizard-scala packages to be com.massrelevance.*
* Change dropwizard packages to match com.codahale.* (back from com.yammer.*)
* Service is now called Application
* Using nl.grons.metrics-scala 3.0.0