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
fix copy&paste bug
fix temperature postprocessor
do not build preconditioner for direct solver
remove debug output
disable pressure normalization for now
disable pressure scaling if using direct solver
Merge branch 'master' into direct_solver
Merge branch 'master' into direct_solver
Changed what appears to be a copy-paste error.
Use introspection in places where block incices had been hard-coded.
Merge pull request #1 from jperryhouts/hardcoded_blocks_patch

Hardcoded blocks patch
Add an interface for an yet to create heating_model in simulator.