New transaction types with memos

[concordium-cl]

Task description The sender should be able to attach text to transfers that will enable him to convey additional information to the receiver. The current use-case mandating this is ease of integration with exchanges.

Sub-Tasks

• Support sending transactions with memos
• Support displaying memos in the transaction list; existing wallets will not display memos on incoming transfers, but will otherwise continue to function fully as they do now.
• Support for new wallet-poxy

New Transfer Types

• simple account-to-account transfers
• scheduled transfers
• encrypted transfers

Backwards Compatibility The change must be backwards compatible. Existing transactions must continue to be accepted by the new protocol, and they must have the same semantics to the extent possible.

EDIT: The flow specifying how this should work, can be found in Figma in "Flow 19"

[jens-concordium]

@concordium-cl, I verified the fixes for Kasper's findings from his memo tests. I guess this can be moved to done now?