Implement the dynamics benchmark winds & currents

[timspainNERSC]

The dynamics benchmark uses an analytic set of wind and current forcings, coded into the benchmark applications themselves. These should be ported to implementations of IAtmosphereBoundary and IOceanBoundary to allow the benchmark to run wholly within nextSIM-DG.

Since the benchmark will need the dummy thermodynamics, I guess this issue is coupled to issue #267.

[timspainNERSC]

Moving to Milestone 2: Functional Tests, since solving this issue is not essential for the merge itself.