Ensure the audio stream transaction is submitted by the player

[reyraa]

Although the Player applications (Web Player and Mobile apps) submit audio stream transactions as designed, being a client app they are prone to manipulations. We should ensure the transactions are submitted as intended. This can be done by the storage API.
The storage API should serve the initial part of the audio to the user to ensure a smooth user experience. After the initial part is delivered, the API looks for the new audio stream transitions on the network and if the expected transaction appears in one of the next 3 blocks, the users can continue streaming. Otherwise the API interrupts the streaming with a relevant error message.