Leave todos.
Update steinberger material model to run with the new material model interface (calling also viscosity for the creation of the adiabatic conditions).
Add experimental support for compressibility in the steinberger material model.
Small bugfixes in lookup class of steinberger material model.
Changed steinberger material model to new interface. Made the incompressible formulation consistent and added a compressible formulation.
Viscosity is now only called if adiabatic conditions is available. No need to check for that in function any more.
Rename some variables for clarity.
Change the simple-compressible test to a more reasonable initial condition.
Made steinberger material model aware of $ASPECT_SOURCE_DIR.
remove useless $Id in code files
Made reference viscosity a user input parameter for steinberger material model.
Document reference viscosity. Set default to old value. Cleanup.
Add a test for the steinberger material model.
Only remove the nullspace in a direction if the user specifies it
Add tests
Hmmm, maybe start counting at one?
fix another test case
Fix typo
update formatting of nonlinear residual

this should fix the test no_adiabatic_heating_03
Add a test utilizing the simple material model for comparison purposes.