Provide Duration APIs as well as (long, TimeUnit)

Several components require setting a duration (for timeouts etc.) that require a `long` and `TimeUnit` pair. Lets provide an API that accepts a `Duration` instead, as it's often less cumbersome to work with, especially when working with a `Configuration` that already provides the value as a `Duration`.

Note: this adds `dropwizard-util` as a dependency of `dropwizard-lifecycle`.