Replacing dropwizard request logging with logback-access

WIP: This isn't ready to merge!

This is an attempt at replacing the Slf4jRequestLog with logback-access, and exposing the log pattern in configuration.

The primary driver behind this is the ability to use more complex log patterns, specifically the %replace(){} function from logback to redact sensitive information from request logs. It also adds the ability to make use of MDC in request logs.

- This relies on [#201](https://github.com/qos-ch/logback/pull/201) and [#202](https://github.com/qos-ch/logback/pull/202) being merged in to logback first.
- It specifies logback-access 1.1.3-SNAPSHOT in the dropwizard-logging/pom.xml because I built logback locally with these changes, obviously this would actually be ${logback.version}.
- This removes the timeZone configuration field as the timezone is now specified as part of the logFormat configuration field instead.
- This needs tests written. I know, I'm a bad person :(

I'm primarily looking for feedback on this. Assuming the logback PRs get accepted, would this be considered?

There is already #370 which has similar goals, but is badly outdated now, and works by adding a new build method to each appender factory, rather than genericising them.