Added license comment too.

The API is going to need some desktop trade utilities, which should be
shared between :desktop and :core.api.

Scope of this refactoring is small;  more can be done, but the short
term goal is to share trade util logic with core api.

- Removed unused method getCurrencyCode()
- Made minor style changes
- Removed duplicated code block

API users will need to see their role as maker/taker when looking at trade details.

- Add getRole(trade) to TradeUtil.
- Add getTradeRole(tradeId) to CoreApi, CoreTradesService.
- Add role field to TradeInfo proto and its wrapper class.

- Move output column header specs to its own shared constants class.

- Add new TradeFormat class for printing trade details in the console.

- Print formatted trade in api trade tests -- to see output before
  using formatter in CLI (in next PR).

Optionally print the json contract for a given trade id.

This PR adds trade closing method stubs to keep funds in the
Bisq wallet or send them to an external BTC wallet.

- Add grpc protos
- Add new methods to GrpcTradesService, CoreApi
- Stub out implementations in CoreTradesService
- Add methods to CLI

The CoreTradesService was refactored to work for newly added api methods:

- keepfunds -- close trade, keep funds in bisq wallet

- withdrawfunds -- close trade, withdraw funds to external btc wallet

A getKey accessor was added to CoreWalletsService (needed by withdrawfunds impl).

Some refactoring of the api test case hierarchy is included in this commit.

This commit fixes non-trade tests broken by the last refactoring.

The implementation will be added to CoreOffersService in the next PR.