Reduce number of dependencies

[alechenninger]

It is occasionally difficult to use the client because it bundles commons-io and jackson.

Commons-io isn't necessary, it could just be refactored away. If Apache http client needs it, we should push that stuff to another module (it's all servlet related anyway -- not client).

Jackson should be part of a bring-your-own-serialization-solution strategy. Other Java HTTP/service clients do this, such as https://github.com/google/google-http-java-client

There are probably others too