Add localintegralenergy.hh and neumannenergy.hh, they assemble the energy for a single element and work with a CompositeBasis

These classes work similarly to Dune::Elasticity::LocalIntegralEnergy and Dune::Elasticity::NeumannEnergy,
where the ones in Dune::Elasticity with a power basis (for the displacement function) and
Dune::GFE::LocalIntegralEnergy / Dune::GFE::NeumannEnergy work with a CompositeBasis (for the displacement AND the rotation),
so the indices to access the different parts of the basis are different.