Debian packaging for envelope-cli #11

Ref. BlockchainCommons/Community#154.

• Create packaging template/instructions for Swift packages. This template will be based on figuring out how to get envelope-CLI to build on Debian Linux.
• Make changes required to make it build on Linux.
  • Some dependencies are specific to MacOS and not cross platform:
    - WolfBase depends on:
    - AppKit: ColorExtensions, DateExtenstions
    - UIKit
    - "bit-for-bit" reconsruction of Foundation.Date doesn't work (according to Wolf's comments). Why? Can we fix it so it works on Linux?
    - BCSwiftSecureComponents-> URKit -> Xoshiro256 -> CryptoKit
    - CryptoKit should be replaced with SwiftCrypto https://www.swift.org/blog/crypto/