ICS-20: add memo field #559
Description
We should also support the memo field, added in ibc-go with cosmos/ibc-go#2595.
Currently, if an ibc-go chain sends a packet with a memo, it will fail on the ibc-rs chain (and the user will be able to recover the funds after the timeout). So supporting it in ibc-rs would make interoperability with ibc-go chains better.