Circumcenter calculation

Currently the calculation of circumcenters is based on a least-squares problem:

For all edges of the entity, formulate pairwise condition

|c - x_i|^2 = |x - x_j|^2, were (x_i, x_j)  forms an edge

with c = lambda * x, i.e. c given in barycentric coordinates. Additionally require sum(lambda) = 1.

The overdetermined system is solved with a qr-method with full pivoting, using Eigen, or row-pivoting using an own implementation. Both implementation fail for some cases, i.e. produce inf or NaN.

This needs to be improved! Find a more stable and maybe more simple way of calculating the circumcenter for an (simplcial) entity of any dimension.