Support additional arguments to Plan::Step

[pangtao22]

State, defined here, is a necessary input to the Step function of all plans. However, different types plans clearly need different fields in State. For instance, TaskSpacePlan only needs the current joint angles, whereas many plan types involving tactile sensing requires measurements from the tactile sensors. The proposed solution is to make State virtual, from which new plan types can inherit can implement their own state.

[pangtao22]

After discussing with Terry, it turns out that this is not a good idea. It would involve lots of changes to IiwaPlanManager, including a config-file-based function call to construct State and lcm subscriptions to the additional measurements.

The alternative is to subscribe to the additional measurements in the new Plan, and store the latest measurements in local private variables. There will be two Step functions, one that's consistent with the declaration in PlanBase, and another deterministic Step that includes the additional measurements in its list or arguments. The first Step is simply a wrapper around the second.