Cardano Registrar Backer

[rodolfomiranda]

I'm submitting this PR as WIP to show how the code is organized and discuss how is the best way to merge all or part of it into keripy.
Summary of what's included:

• new kli backer start command to start the backer
• new kli backer info command to get backer info
• new kli backer query command to query the KEL from the blockchain for a given prefix
• new backering.py file: it's a based on code from indirecting.py and calls publishEvent from the ledger class when a KE receipt is requested
• new folder ledger with a new cardaning file/class that handles Cardano operations
• new backer folder into \demo that includes several backer demo scripts

cardaning class code were improved from last demo and includes the following features:

• Cardano Address is derived from the same Ed25519 seed (private key) used to derive the prefix of the backer. No need to manage/store extra keys now.
• Allows anchoring KELs from multiple prefixes as Transaction Metadata into Cardano Blockchain
• Queue events during a period of time to wait for several block confirmations as a safety measure. Also avoids disordering of KE and duplicates.
• Fix order of Key Event labels
• Optional funding address to fund the Cardano address of the backer
• Depends blockfrost-python sdk to interact with the cardano blockchain. It requires an API KEY. That's one of the reason to consider hosting this class in a separate repository.
• Depends on pycardano library to serialize cardano transactions

[rodolfomiranda]

This PR can be closed. The Cardano Registrar Backer is moving to RootsID repo cardano-backer to keep keripy clean of non keri core code.

[pfeairheller]

Closing because the work has been moved.