Adjustments to JerseyClientBuilder to use configuration options otherwise ignored

Please see issue #557 in the issue tracker.

The basic problem was that the DW JerseyClientBuilder didn't properly take into account a lot of the configuration options you can pass to a Client object, particularly the proxying features.  This uses code taken from ApacheHttpClient4 to process those configuration options and get them into the ClientHandler object so they'll be properly picked up.

This is my first pull request, so apologies if I did it wrong.  :)
Please use the SLF4J [Logger](http://www.slf4j.org/apidocs/org/slf4j/Logger.html) like the rest of the Dropwizard project.