Add smart contract wallet

[DOBEN]

Purpose

closes #412

Next: Update the CIS5 standard proposal document to match the reference implementation:
Concordium/concordium-update-proposals#60
e.g. the service fee is deposited to the public_key of the service fee recipient in this implementation to avoid too much dust amounts being sent to addresses.

Changes

Add smart contract wallet reference implementation.

[Bargsteen]

Nice work ;)

[DOBEN]

I decided to change the from_address in the receiveHook function call in the cis2_multi contract. This chain seems to make more sense in terms of the token being moved from one address/public_key to another. The DepositCIs2TokensEvent is logged before the MintEvent but both events are in the same atomic transaction.

Event flow of depositing cis2 tokens into the smart contract wallet is as follows now:

MintEvent (in cis2_multi contract) -> to to_address
DepositCIs2TokensEvent (in smart_contract_wallet contract) -> from to_address to alice_public_key.

concordium-rust-smart-contracts/examples/cis2-multi/src/lib.rs

Line 1044 in e5f590f

from: Address::from(address),

[limemloh]

LGTM 👍