Only include the multiplication of a ScaledIdentityMatrix with another FieldMatrix if dune common is older or equal 2.8

Add multiplication of a ScaledIdentityMatrix with another FieldMatrix to the collection in linearalgebra.hh

Several energy density implementations contained code for matrix methods
like sym, skew, transpose etc.  This patch moves them all to the file
linearalgebra.hh, to get rid of the redundancy.

In favor of the new ones in dune-common.

The dune-common 2.7 release finally adds all those standard
binary addition, multiplication, etc operators for FieldVector
and FieldMatrix.  Hence we do not have to have our own
implementation anymore.  We still keep it for backward-
compatibility with dune-common 2.6, but guard it behind
cpp conditionals.

They only make sense if the 'adouble' type is known.

This patch adds several more implementations of operator+ etc for FieldMatrices.
In particular, you can now combine matrices of adoubles (the 'active' type from
the ADOL-C automatic differentiation library) with regular double types.

These new operators are needed for the NonplanarCosseratShellEnergy class,
which is coming in the next patch.

[[Imported from SVN: r7561]]

[[Imported from SVN: r7547]]