Unify LagrangeSimplexFiniteElement across dimensions

The LagrangeSimplexFiniteElement contains 5 different code paths to implement the basis and its derivatives:

• A special implementation for order 0 in any dimension.
• A special implementation for order 1 in any dimension.
• An implementation for any order in dimension 1.
• An implementation for any order in dimension 2.
• An implementation for any order in dimension 3.

There are good reasons for the first two special cases. Unfortunately the ones for dim=1,2,3 are all implemented differently for no good reason (except history) makes the code hard to read and understand.

This patch unifies the latter three implementations. While there are still three branches, there is a very simple common structure making the now making the code much simpler to understand. The unified implementation basically follows the former evaluateFunction() implementation of the 3d case:

1. Rescale the simplex by k such that Lagrange points have integer coordinates.
2. Transform to barycentric coordinates in the scaled simplex.
3. Loop over Lagrange points in lexicographic order.
4. Compute basis functions as products of univariate Lagrange-polynomials wrt. barycentric coordinates.

This approach is now also used for evaluateJacobian() and first order derivatives in partial() extending the support of the latter to dim=1 and dim=2. arbitrary order partial derivatives in partial() for dim=1,2,3-

For now the special implementation of second order partial derivatives in 2d is kept, but could be updated accordingly.

This includes the cleaned up test from !293 (merged). Hence the latter should be merged before.