Documenting and modeing PCB stackup shield materials in Speedstack

Documenting shields in Speedstack

Adding shielding materials to stackups in Speedstack is enhanced post version 21_02 with the addition of dedicated shield material type in the library. Impedance and insertion loss modeling is also adapted to ensure the Df and Dk of the adhesive layer are included in the modeling - especially when using shields denoted "for high speed applications"