Migrate from dune-fufem to dune-functions bases

- local energies and assemblers depend now on the localView, instead of the element and the localFiniteElement
- the basis is now assumed to be a powerBasis (dune-functions compatible)
- this features flat element vector and matrix types and simplifies the implementation
- all affected classes are now in the Dune::Elasticity namespace

- for backwards compatibility, old implementation are kept in the "Dune" namespace and deprecated messages are placed
- the TrustRegionSolver is also capable of the new powerBasis

- TODO: dune-parmg is still hardwired to scalar basis types, therefore usage is not possible with the new basis