Make the code dimension-independent
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Much of the code is already dimension-independent. However, the following major things are left:
- Mesh structures. This will probably be the most time-taking part. Needs new indices in some mesh connectivity structures.
- Numerical fluxes. The Roe and HLLC fluxes are still not dimension-independent.
- Wall boundary conditions. These need to be generalized to 3D. For now we allow setting a "tangential" velocity at the wall. This will not be possible in 3D. We might just want to restrict this to zero velocity at the boundary.
- Free stream state needs a sideslip angle as well.
The rest should be reasonably straghtforward.