*`*NodeFactoryBuilder` will be named `*BasisFactory`. This fixes #13.
* We should implement `PkPreBasis`, `QkPreBasis`, `Lagrange::p<k>()`, `Lagrange::q<k>()`. `lagrange<k>()` should (if possible) create `PkPreBasis` or `QkPreBasis` if this can be derived from the grid view.
*`namespace Dune::Functions::BasisBuilder` should become `namespace Dune:Functions::Bases`.
*`LocalIndexSet::bind()` should fill an internal cache with the indices. `LocalIndexSet::index()` should be cheap and only look up the index in the internal cache. This can be implemented now in `DefaultLocalIndexSet`.
*`NodeIndexSet` should be extended by a method for batch filling all indices into an external buffer.
