[trello.com/c/QSbUdocE]: KlyWalletService tests

[ChrisBenua]

KlyWalletService test.

For testing purposes KlyNodeApiServiceProtocol and KlyTransactionFactoryProtocol were introduced.

For testing URL-request inside sendTransaction RpcRequestBody was used. To return real response body, I've used KlyTransactionSubmitModel.

Because LiskKit inside uses private URLSession, default practice using MockURLProtocol won't work, because it requires to instantiate URLSession with custom URLSessionConfiguration. So I've used swizzling for mocking URLSession.init. Because internally URLSession.init is actually class method, so for swizzling we should exchange two class methods implementations:

guard let originalMethod = class_getClassMethod(URLSession.self, originalSelector),
           let swizzledMethod = class_getClassMethod(URLSession.self, swizzledSelector) else { return }

Inside swizzled method we change actual URLConfiguration with custom URLConfiguration with mocking using MockURLProtocol