Implement total Darcy flux calculation and minor build-system cleanup

This change-set takes a first cut at implementing a total (Darcy) flux calculation in `ImpesTPFAAD.hpp`.  It is compile-tested only.

There are also some unrelated changes that mostly fix white-space issues and include `test_impestefa_ad` amongst the `examples` that are currently built.  Otherwise, we don't even get build-testing of the `ImpesTPFAAD` class.