Validate the state changes for the Delivered and Processed sender

[hackaugusto]

The state changes that correspond to the delivered and processed message must have the address of the sender, this address must be authenticated by some means that are dependent to the transport layer (currently the message itself contains a signature which must be recovered)

• Add the sender to the Delivered and Processed state changes

• Update the node.py handle_delivered to validate the sender

• Update the node.py handle_processed to validate the sender

• Create a marker state_change which all Receive* state changes inherit from

• Remove "authentication" check (sender == recipient) from the transport and leave it to the state machines.

[andrevmatos]

Related to #2295