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
add another main goal in the documentation
Merge pull request #9 from tjhei/editmanual

add another main goal in the documentation
Merge branch 'master' into direct_solver
Fix forgotten resizing of depth average files. Add an assertion.
Merge pull request #10 from bangerth/fixes

Fix forgotten resizing of depth average files. Add an assertion.