[Typetraits] Follow dune-common transition from SelectType to C++11-like conditional
[Headercheck] Don't include function.hh from typetraits.hh to avoid an invalid circular inclusion

function.hh includes TypeTree headers which in turn require typetraits.hh for
decltpr<>(), so let's not do that. Apart from that, having typetraits.hh depend
on the much higher-level function.hh smells like bad layering...
Merge branch 'work'

Just some small fixes

* work:
  [Headercheck] Don't include function.hh from typetraits.hh to avoid an invalid circular inclusion
  [Typetraits] Follow dune-common transition from SelectType to C++11-like conditional
[TypeTree] Switch to external TypeTree library
[ISTLMatrixBackend] Fix compilation error in constructor that assigns an initial value
[VectorGridFunctionSpace] Reimplement name() getter to avoid visibility problem
[Tests] Fix warnings about moved constraints headers
[Tests] Add missing include statements to fix some compiler errors
[Tests] Disable tests that have been known to fail forever because of non-ported features
[Tests] Fix test failures due to new handling of nested function spaces and orderings
[Whitespace] Clean up functionwrappers.hh
[Whitespace] Clean up testutilities.cc
[VectorGridFunctionSpace] Fix construction sequence to avoid segfault related to now handling of function space tree

The GridFunctionSpace base class now assumes that the underlying tree is correctly
initialized with valid objects by the time its constructor is called because it has
to propagate information down that tree.
Unfortunately, the VectorGridFunctionSpace postpones the creation of the per-component
child spaces until after that constructor call, causing a segfault.

This patch fixes the problem by moving the population of the storage array to a static
helper function that gets called earlier in the sequence.
Merge branch 'work'

Lots of small fixes that have come out of trying to run the testsuite
in the aftermath of splitting of the TypeTree library.

Most of the fixes are local to the tests, but there are two external
fixes

- VectorGridFunctionSpace was broken after the recent changes to the
  way nested spaces work

- the ISTLMatrixBackend constructor that directly assigns a value didn't
  compile

* work:
  [VectorGridFunctionSpace] Fix construction sequence to avoid segfault related to now handling of function space tree
  [Whitespace] Clean up testutilities.cc
  [Whitespace] Clean up functionwrappers.hh
  [Tests] Fix test failures due to new handling of nested function spaces and orderings
  [Tests] Disable tests that have been known to fail forever because of non-ported features
  [Tests] Add missing include statements to fix some compiler errors
  [Tests] Fix warnings about moved constraints headers
  [VectorGridFunctionSpace] Reimplement name() getter to avoid visibility problem
  [ISTLMatrixBackend] Fix compilation error in constructor that assigns an initial value
[Documentation] Document new dependency on dune-typetree
Merge branch 'feature/remove-typetree'

As the title says: TypeTree is now an external dependency.

* feature/remove-typetree:
  [Documentation] Document new dependency on dune-typetree
  [TypeTree] Switch to external TypeTree library
Fixed spelling
Organize includes.
Replace instances of conditional by Dune's SelectType.

The uses of conditional were unqualified and thus could not work.
Add forgotten transition header for interiornodeconstraints.hh.