This will later simplify merging the mixed and non-mixed versions
of the assembler code.

Using LocalIndexSet objects was mandatory with dune-functions-2.5
and earlier.  However, we only support 2.6 and later anyway,
so let's get rid of the backward-compatibility code.

This is how the new dune-functions bases should be used.  Also, it is yet
another step towards merging CosseratEnergyLocalStiffness and MixedCosseratEnergy.

Because this object doesn't exist in dune-functions bases anymore.

Conceptually cleaner, and makes for simpler code.  Most importantly, we will want
to pass the Basis::LocalView to the local assemblers.  For that we need the actual
basis, not just the grid view and local finite element.

[[Imported from SVN: r10082]]

At least the harmonicmaps.cc example still works as before.
[caveat: only tested without HAVE_MPI]
Internally, at various places in the code, a dune-fufem basis is still constructed
from the dune-functions one.  These parts can be ported one by one, as dune-fufem
slowly replaces its own bases by the ones from dune-functions.

[[Imported from SVN: r10080]]

[[Imported from SVN: r9853]]

This does what we want both on one and on many processors.

[[Imported from SVN: r9707]]

Because the gradient is needed anyway when computing the Hesse matrix.
Not computing it separately a second time shaves off about 8% wall time
of each iteration.

[[Imported from SVN: r9555]]

[[Imported from SVN: r9392]]

[[Imported from SVN: r8199]]

[[Imported from SVN: r7837]]

[[Imported from SVN: r7611]]

and barycentric coordinates.  This is easy because we know the
number of element corners at compile time (I currently don't
see support for non-simplex elements at all).  This saves 
time, but not much: about 1%.

[[Imported from SVN: r7550]]

[[Imported from SVN: r6209]]

Compute the local corrections in local coordinates on the tangent bundle now, instead of using the embedding in the surrounding space

[[Imported from SVN: r5985]]

[[Imported from SVN: r5966]]

For this now the TangentVector class of S^n has only n components,
while the EmbeddedTangentVector class still has n+1.
The code around it needs to be fixed accordingly.

[[Imported from SVN: r5963]]

[[Imported from SVN: r5931]]

[[Imported from SVN: r5690]]

[[Imported from SVN: r4080]]

[[Imported from SVN: r4063]]

[[Imported from SVN: r4055]]

[[Imported from SVN: r4038]]

[[Imported from SVN: r4030]]

[[Imported from SVN: r4024]]