Add helper script and input files for some simple unstructured meshes
Attempting to make a driver where all relevent options cant be set from scripts

* Should make experimentation much easier, no more messing with c++

* Use factory methods to convert cli -> templated things

* Includes an initial python control script (for parameter sweeping)
Some improvements/fixes for the midpoint methods

* Fix nprev_values() to allow larger n_interp

* Rename OldMidpointMethod -> BDFMidpointMethod

* Fix include guard in old_midpoint_method

* Improve constructors