Process `Withdraw` actions in the ICS20 component

[hdevalence]

To handle a withdraw action, we need to:

• [ ] Create an appropriate FungibleTokenPacketData from the action contents;
• [ ] Add the packet to the chain state in a way that's legible to the counterparty chain;
• [ ] Somehow register a hook to process either an acknowledgement or a timeout;
• [ ] Add logic to return funds in the event of a timeout.

Spec link: https://github.com/cosmos/ibc/tree/master/spec/app/ics-020-fungible-token-transfer#packet-relay