- Introduce class `LocalDensity` for material-specific implementations
- Introduce class `LocalIntegralEnergy` to work with the densities
- Local energies and FE assemblers use now `dune-functions` power bases instead of scalar `dune-fufem` bases; the key element is the `LocalView` which contains the information for each element
- Introduce class `LocalHyperDualStiffness` and `hyperdual` to calculate gradient and hessian using hyper-dual numbers