Constraints parameter classes are basically just grid functions returning
bools. Going through interpolate.py reduces lots of reduntant code.

Working:
- Driver block
- Solving and visualization

Not working:
- Error calculation

These methods are part of the driver block class interface and should also be
generated if they are not used from the main function.

In many places we treat this as codegen-time information anyway.
For loopy, this is the necessary way to go.

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

Instationary stuff not fixed so far.

To comply with latest pdelab.

Do not annotate FiniteElements anymore, further split driver code

Do not annotate FiniteElements anymore, further split driver code