WIP Test/nonisothermal

See !2473 (closed). Based on !2471 (merged)

Shows unphysical temperature gradient.

• See if we can get a better solution by adding \vec{v}\cdot\nabla p in the energy balance somehow

For incompressible fluids we have at least two options:

• Assemble internal energy fluxes instead of enthalpy fluxes, the volume work term disappears (not generic)
• Add the missing term and keep assembling enthalpy fluxes

There might be other solution by inserting the continuity equation to turn the term into some time derivative.