Implement TansactionMailing

  - Begin deprecation of `Batch` in favor of `BaseMailing` template for `BatchMailing` & `TransactionMailing`
  - Use fail keyword instead of raise unless rescuing
  - Transaction mailing implementation
  - Refactor HTTP
  - Refactor XMLBuilders
  - Add TransferProtocol base class
  - Refactor TransefProtocol child classes