Update token whitelists

[sug0]

Implement the Ethereum token whitelist logic in Namada.

The Ethereum token whitelist is only stored and acted upon in Namada, after crossing the bridge over from Ethereum. This means that we are able to receive transfers from non-whitelisted assets, or from assets whose token caps have been reached in Namada. In these cases, NUTs (Non Usable Tokens) should be minted in Namada, instead of wrapped ERC20s.

Tasks

• Mint NUTs
• Burn NUTs after transferring them out of the Bridge pool
• Test minting/burning of NUTs and wrapped ERC20s with unit tests
• Add NUT native VP to reject NUT transfers between accounts other than the Bridge pool
• Test NUT native VP
• Update Bridge pool VP to check NUT escrows
• Test Bridge pool NUT escrows
• Update the CLI to allow building NUT transfers to the Bridge pool
• Allow Ethereum token whitelist to be configured through the Namada genesis file
• Update the smart contract code to reflect the new design

[sug0]

Related to #1234