Add aiken example

[j-mueller]

This PR does two things:

1. Change the structure of the offchain code, separating the CIP-143 code from the WST example. There are now three packages for CIP-143 (programmable-tokens-onchain, programmable-tokens-offchain and programmable-tokens-test). The WST code lives in the regulated-stablecoin package.
2. Add a CLI tool cip-143-cli . This is a tool for managing CIP-143 policies. See README for details.