Add global statistics postprocessor

[gassmoeller]

This is a rebase from #1429. I will need to adjust the test outputs because of our switch to the 8.5 tester.

[gassmoeller]

This should be ready for review/merge. For earlier comments that are addressed see #1429.

[bangerth]

You no longer need the distinction here (i.e., just use SolverControl unconditionally) because for old versions of deal.II, writing SolverControl finds the declaration in namespace aspect, whereas for new versions of deal.II, it just takes the one in namespace dealii because there is none in the "closer namespace" aspect.

[bangerth]

just say

  namespace aspect {
    class SolverControl : public dealii::SolverControl

and you won't need the typedef below any more :-)

[gassmoeller]

I addressed the comments, and it seems to work. Dont know why it did not work the first time I tried it that way. Anyway, should be ready to merge now.

[tjhei]

This PR broke mainline:

In file included from /home/dealii/source/include/aspect/global.h:48:0,
                 from /home/dealii/source/source/boundary_composition/interface.cc:22:
/home/dealii/source/include/aspect/compat.h: In constructor ‘aspect::SolverControl::SolverControl(unsigned int, double, bool, bool)’:
/home/dealii/source/include/aspect/compat.h:53:55: error: constructor delegates to itself
         SolverControl (n, tol, log_history, log_result)

[bangerth]

On it.