Update compiler to Java 1.7

Upstream Dropwizard has made the jump to Java 7, so we should too.
Switch to com.codahale namespace and metrics 3.0.0

0.7.0 and metrics 3.0.0 are both under the `com.codahale` namespace, not
com.yammer.
Fix everything to work with new 0.7.0 API

Regression:
    * `dropwizard-extra-kafka` - `MessageProcessor` no longer times
    iterations. You will need to do this explicitly in your
    `MessageProcessor` until a new API is devised.
Fix Configuration tests to use Jackson helper

`Jackson.newObjectMapper()` should be used to create `ObjectMappers`
that are configured for use in Dropwizard.