consider more utils for testing contracts

[marc0olo]

e.g.

• withFee, see https://github.com/aeternity/state-channel-demo/blob/develop/contract/test/game.test.js#L29
  • not sure about the naming here as it only returns the used fee
  • also it could be convenient to return more data, not only the fee (gas price, gas used, ...) which doesn't have to be extracted separately from tx-result if there is no interest in any other data of tx-result
• failsWith, see https://github.com/aeternity/state-channel-demo/blob/develop/contract/test/game.test.js#L59

anything else important @bogdan-manole?

what's important and generally usable in https://github.com/aeternity/lqty-contracts/tree/feat/lqty/test/shared/utilities ?