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.

[ ] Go through system part -> GFS
[ ] Export boundary grid function

A pattern that we have been manually implementing in quite some places!

This is not used anymore since we have mixins.

IT is both simplicial and quadrilateral...

So far, we were a bit sloppy about which basis we choose from the UFL
counterpart. This commit implements the necessary 1-to-1 mapping.

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

This reverts commit 6a1e7cc9

This reverts commit f83a804e

The Exadune preconditioners cant handle one sided assembly for reasons.