This variable is intended as a library wide flag to enable profiling and
can (/should) be used to guard profiling of library code.

If the user defines DUNE_STUFF_ENABLE_PROFILE_SCOPE=1, the macro
`DUNE_STUFF_PROFILE_SCOPE("section")` is defined an creates an instance of
`ScopedTiming`. This can be widely used without cluttering the code too
much, see for instance the next commits.

Conflicts:
	dune/stuff/test/grid_periodicview.cc
	resolved by using local version

now outputs csv style key/value table

...so I can to_string Yaspgrid indices

Historically it was possible to create any type of vector of any requested
length from an expression of the form "1" or "[1]" by interpreting this as
the scalar 1 and filling all components of the vector with this value. That
somehow got lost in the re-factoring of string/configuration; this commit
restores the old behavior.

We could argue, though, that we only want vectors of arbitrary length to be
created from "1", not from "[1]", as the latter looks like an explicit wish
for a vector of length 1.

Since we cannot assume that operator<< is implemented for T

Reapply 9057c24, somehow that one got lost^^

This reverts commit 273490bb3dc7db95dbc82278099d82b31c2f8285.

This is used in some tests to give further useful information (for instance
in the EOC runs in dune-gdt). On the other hand this output is naturally
suppressed by `make test` and only shows up in the detailed test output, so
it should not bother anyone.

If defined, all output is suppressed. This can also be used to disable
large tests.

This reverts commit eb86eee984198069e4c120d8329990b9cf9ae9ac.

Conflicts (resolved to remote branch):
	dune/stuff/fem/customprojection.hh
	dune/stuff/fem/error.hh
	dune/stuff/fem/functionadapter.hh
	dune/stuff/fem/functions/checks.hh
	dune/stuff/fem/functions/integrals.hh
	dune/stuff/fem/functions/magnitude.hh
	dune/stuff/fem/functions/timefunction.hh
	dune/stuff/fem/localmatrix_proxy.hh
	dune/stuff/fem/restrict_prolong.hh