ETH delivery punchlist

[placer14]

In response to requests/responses posted in #1666 (https://gist.github.com/amangale/2d91c8dc4eb95a1fdf34363b83cf901d).

General thoughts:

• We probably want inputs and outputs showing the full definition, though it's probably okay to allow inputs where a currency string is offered to continue allowing it OR provide another key with the full definition so a different divisibility could be used if desired. If the full definition is provided in key currency then the string could provided instead inside currencyCode in a parallel key which defaults to the node's definition of that code.

Items which need to be resolved as part of the ETH milestone:

• GET /wallet/balance should indicate TETH properly (currently shows as ETH)
• GET /ob/listing, GET /ob/listings, and POST /ob/listing all have representations of the currency symbol where we probably want to show the full definition.
• POST /ob/orderspend: The amount has another nested amount and we probably don't want to be redundant. Maybe that outer amount should be payment? We might consider the same change in the response body as well. Ex:

    {
	"wallet": "ETH",
	"address": "0xC8Be18369A30918FE8Bb950A9496A8269992aa0c",
	"amount": {
            "amount": "4049405570649999",
            "currency": {
                "code": "ETH",
                "currencyType": "crypto",
                "divisibility": 18,
                "name": "Ethereum"
            }
        },
        "orderId": "QmUm92zCropp3dmN6JPdFfm38mjN5XnXTGdAPEpdvMfyDe",
	"feeLevel": "NORMAL",
	"memo": "Yo"
    }

• POST /ob/purchase input JSON for paymentCoin should be full definition
• GET /ob/order/:orderId should return full definitions for acceptedCurrencies

Bonus:

• Stop using models outside of the API package within requests/responses
• Extract more behavior out of the API package