pcb-material definition represents a material in a
pcb-material material-identifier : name: String description: String type: Conductor|Dielectric dielectric-constant : Double
name field is an optional name associated with the material that is different from its identifier.
description field is an optional string describing the material.
type is either
Dielectric, representing what kind of material this represents.
dielectric-coefficient is an optional double value representing the permittivity of the material.