(WIP) -- Contact-Homotopy Updates (Cache results of Tribol calls, Non-tied contact, etc).

[thartland]

This PR adds

• initial caching of results from Tribol contact mechanics computations. That is, repeated calls to the same function at the same point will not lead to additional contact mechanics computations.
• complete caching of results from Tribol mechanics computations. That is, when the gap constraints are evaluated internally Tribol also computes gap constraint Jacobians.
• an example of non-tied contact wherein the contact complementarity system is solved directly and does not make use of a reformulation of the nonlinear contact system by penalizing contact.

Regarding item (2) -- there is now a structure in the Constraint class to communicate that we are requesting a "fresh_derivative" but not at a "new point". By "new point" we mean has the Constraint class "seen" this point in it's most recent computation (perhaps as just a constraint evaluation), so that a derived Constraint class can cache the Jacobian computations from the constraint evaluation and just provide the cached Jacobian when a "fresh derivative" is requested at an "old point".