[DOFMapper] Fix deprecation warning
[CouplingGFS] Remove dead leftover code

DataHandle stuff is now handled by the DataHandleProvider mixin, and the
already disabled update() method doesn't even have archaeological value
anymore...
[CouplingGFS] Adjust to new GridFunctionSpaceBase API

- Add ordering tag to constructor signature
- Forward ordering tag and backend tag to base class
[CouplingGFS] Drop backend instance

The backend instance is now stored by the GridFunctionSpaceBase mixin,
so we don't have to do it manually anymore.
[CouplingLFS] Make data members public so they can be accessed by the PDELab visitors

Most of the actual funtionality of the local function space is
implemented in a couple of TypeTree visitors that we reuse unchanged
from PDELab. Those visitors need access to the internals of the LFS, but
unfortunately, they live in an anonymous namespace, which makes it
impossible to declare them as friends outside of their own source file.

So we just take the dirty way out and make everything in CouplingLFS
public; if anyone is stupid enough to play around with those members,
they deserve what's coming for them.
[CouplingLFS] Remove defunct method mwrite()

Another relic from the stone age...
[CouplingGFSOrdering] Fix method names

At some point in time map_index() in the ordering interface was renamed
to mapIndex() and map_indices() to map_lfs_indices(). This patch
implements that change for the CouplingGFSOrdering.
[CouplingGFSOrdering] Inherit from PartitionInfoProvider

Orderings must provide information about the contained parallel
partitions. Inherit from PartitionInfoProvider to add the required
functionality.
[CouplingGFSOrdering] Integrate support for GFS data update mechanism

Orderings update some information in the GFS (sizes in particular) via a
callback mechanism that is implemented in the Ordering base class, but
needs some support in the Ordering implementation. This patch adds those
support bits to CouplingGFSOrdering.
[CouplingGFSOrdering] Replace deprecated IndexSet::geomTypes() with IndexSet::types()
[Tests] Fix testmortarpoisson

Take care of the bitrot...

- q1fem -> qkfem
- qkfem needs a GridView, but there is no GridView for the mortar space,
  so we just create a minimal PseudoGV that only exports the
  dimension (the q1fem doesn't need anything else)
- The subdomain conditions now use a std::initializer_list for the list
  of subdomains instead of their weird variadic constructor
- SubDomainIndexType -> SubDomainIndex
[Tests] Silence compiler warning in testmortarpoisson
[PowerCouplingGFS] Update to work with improved PowerCompositeGridFunctionSpaceBase

The PowerCompositeGridFunctionSpaceBase mixin now expects both the
ordering and the backend tags in its template parameter list and also
requires the derived class to pass instances of both types in the
constructor. So this patch changes all constructor signatures of
PowerCouplingGFS to accept instances of those two types. Apart from
that, it also fixes the interface to the Ordering to do the whole
create-on-demand thing.
[PowerCouplingGFS] Make PowerCouplingGFSTag inherit from PowerGFSTag

And by the magic of TypeTree and its weird but clever transformation
registry, we inherit the correct LFS behavior from PowerGFS.
[MultiDomainGFS] Re-enable gfs_flavor_tag specialization for PowerCouplingGFS

Now that PowerCouplingGFS compiles again, we have to make sure it gets
recognized by the visitor dispatch mechanism in
MultiDomainGFS. Otherwise *really* weird stuff happens...
[Tests] Fix testpowermortarpoisson

Even more bitrot in this one

- q1fem -> qkfem
- qkfem needs a GridView, but there is no GridView for the mortar space,
  so we just create a minimal PseudoGV that only exports the
  dimension (the q1fem doesn't need anything else)
- The subdomain conditions now use a std::initializer_list for the list
  of subdomains instead of their weird variadic constructor
- SubDomainIndexType -> SubDomainIndex
- Adjust to new Poisson interface
- Switch to new matrix backend
- Don't use subspaces for VTK output
- Port over VTK output from testmortarpoisson, the stuff that was in
  this one has been dead for ages
- Silence compiler warnings about unused variables and typedefs
Add includes to almost fix headercheck.

powercouplinggridfunctionspace.hh still fails.
Fix building tests.
[CMake][Tests] Don't build reactiondiffusion and stokesdarcy, they are broken
[Tests] Fix running test(power)mortarpoisson without command line arguments

These two tests require two run time parameters, but simply segfaulted
if they were missing. Clean up that mess and provide default values to
make them usable as actual tests.