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...

We run ut of PIDs during a typical run on KNL.

Additionally, uses the right number of subrefined intervals in the blockstructured case

Still not beautiful...

This reverts commit b82e6531.

for consistency.

Otherwise debugging of nonlinear problems becomes hard.