Feature/code restructuring

All the restructuring stuff we talked about.

Tested.

See merge request !38

refactoring pullback loopy update

This MR will supersede !34 and !27 as I created a big mess while working on those two.

See merge request !36

We do not need it.

Various fixes, including diagonal jacobian transformations.

Feature/sumfact amatrix

Create Theta matrix for sumfactorization in constructor.  This is just a starting point for further implementations.

See merge request !37

Test cache behaviour



See merge request !35

Remove symbol (didn't rebase the first time)

I didn't rebase the first time so I missed some new symbols comming from nonlinear jacobian apply.

See merge request !33