Add config for dataverse-client-r

[wibeasley]

Similar to issue #17 involving the JavaScript client, @pdurbin has suggested that Jenkins incorporate the R client.

I don't know much about Jenkins, but the package probably isn't ready in its current state, because the test suite is hard coded to hit demo.dataverse.org, and I imagine it needs to be configurable to hit the temporary image spun up by Jenkins?

This roadmap should describe what needs to be developed within the R package before Jenkins can incorporate it effectively.

(Please tell me if I need to adjust some roadmap.)