List simulated external transactions

Retrieve a list of all simulated external transactions. These
transactions can be created using the POST operation or they may be
created by interaction with the core Conduit API.

Examples:

• When creating a withdrawal transaction in through the core API in
  the sandbox, a corresponding simulated external transaction will
  be created to allow control of the outbound transaction.
• In order to deposit assets into a sandbox account using a push
  transaction a simulated external transaction should be created
  using the /sandbox/transactions API.