Note: This is still structured for now

So far, we had the opcounter cast to Dune::FieldVector
of size 1. Now it defines the correct type.

As a step towards making the driver the main function.

It makes the code generation workflow more complicated without
contributing anything substantial

Instationary stuff not fixed so far.

The previous name was *really* confusing.

Much more telling name...

There is way more reasons to interpolate a function into the
solution vector and we cover them with one code path:
* Dirichlet boundary conditions (strong ones)
* Initial conditions for instationary expressions
* Initial guesses for Newton solvers

These might sound completely silly, but they are useful when writing
code generic w.r.t. the number of components

It has single precision support...