Updating Jackson to 2.4.0

Minor release with new functionality but backwards compatible.

- Official support for Guava HostAndPort (removed Dropwizards deserializer)
- Jdk7Module with support for Path
- Bunch of misc improvements

https://github.com/FasterXML/jackson/wiki/Jackson-Release-2.4

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It looks like Jackson 2.4.0 actually has a [couple regressions](https://github.com/FasterXML/jackson/wiki/Jackson-Release-2.4.1) from 2.3.x, so it may be worth holding off merging this until 2.4.1 is out and going straight to that. Thoughts?