add TemperatureOrComposition::component_index
start work on DirectSolver by putting u+p into one block

Still incomplete, have to fix many other places that assume specific
blocks. I had to rework Introspection::BlockIndices for this.
rework initial temperature conditions to use component_index
Merge branch 'master' into direct_solver

Conflicts:
	source/simulator/initial_conditions.cc
	source/simulator/introspection.cc
fix merge
fix advection assembly blocks
fix block indices in several places
remove debug output
merged in Timos initial modifications.
fix copy&paste bug
fix temperature postprocessor
do not build preconditioner for direct solver
remove debug output
Trying to keep up with Timos modifications. This merge doesn't really work.
disable pressure normalization for now
disable pressure scaling if using direct solver
Again, keeping up with Timo.
Merge remote-tracking branch 'timo/direct_solver' into jph-direct_solve
Fixed merge. Aspect compiles now, but fails after a few timesteps.
Generalized the VectorFunctionFromVelocityFunctionObject constructor for cases with porosity.