Tempus: Add potential full-space optimization interface.
Created by: etphipp
This PR adds a transient full-space optimization interface to be used with packages such as ROL with its DynamicConstraint interface. An implementation of the interface is provided by BackwardEuler only (currently). A test that the interface computes what one would expect for BackwardEuler is also provided. The idea is to then implement ROL's DynamicConstraint interface using Tempus, and then continue to develop and refine the interface.
The interface should easy to implement for any multistep method. It is not yet clear how multistage, 1-step methods should be handled. This PR also does nothing with the objective, since Tempus has no interface for integrating responses (as far as I can tell).