Address JSON-LD semantic issue for Commercial Invoice

[BenjaminMoe]

From: #808

We deleted Proforma Invoice and added a boolean flag to Commercial Invoice Credential.
The boolean flag works in schema-land, but it's bad semantics.

The scope of this issue to propose a solution for how semantics could be better applied to the boolean flag.

[BenjaminMoe]

Would like input from someone consuming the n-quad view of these credentials @nissimsan .