Add support for Joda DateTime objects to jDBI.

This is a pretty close duplicate of @nicktelford's pull request codahale/dropwizard#304

Given Dropwizard's tight integration with joda-time, this feels like a great feature to have integrated into the Dropwizard toolkit.

I added a small blurb to the documentation (similar to the notice about Guava support) so that it's obvious to JDBI users that this integration is available.