Remaining tasks

[danfinlay]

• Enforce replay protection for invocations
• Allow chains of >1 delegation
• Add caveat support, start with a simple one (like "allowed method").
• Add a few interesting caveats (allow list, call limit, erc-20 allowance)
• #7
• Consider if there is an acceptable gas-payment strategy we can take here, (maybe ensure a user can sign a payment to the submitter in the same batch, which would require a batch be able to include an invocation for another contract).
• Maybe add some reference classes that inherit from Delegatable, like ERC-20 and Ownable.
• Make a sample dapp that enables a basic delegation + recursive invite flow.
• Make a snap to enable making caveats more readable
• Make caveat displaying snap itself expose an extensible API, so other snaps can render other caveats.