Speed up construction of the ClebschGordanProduct class and introduce a high default for param max_angular.

[jwa7]

Currently, construction of a ClebschGordanProduct object involves calculation of CG coefficients with wigners and then some processing, namely: real <-> complex conversion, reshaping into sparse/dense formats, and wrapping in metadata for storage in a TensorMap. While the computation itself is fast, the code for processing was inherited from (very) old versions of the CG code, and is slow and scales poorly with max_angular. Profiling and redesign of this part of the code is required and, once faster, introduce a high default value for max_angular (~ 30 - 50) to make usage of ClebschGordanProduct and wrapping classes more user friendly.