echo_node has to depend on get_payment_events_for_token

[CosminNechifor]

Problem Definition

After the changes I did in #2038 where the payment endpoint was added, the echo_node has to be changed, at the moment it uses get_channel_events which returns more then just the payment events. It should use the get_payment_events_for_token.

This brings us to another problem, we should adapt the logic of the echo_node... previously the get_channel_events was returning a dictionary and now the get_payment_events_for_token returns a tuple.

Proposed solutions

Change the logic of the echo_node to ensure it works with the output provided by get_payment_events_for_token, or convert the returned values to match the previous types.

[palango]

Fixed by #2165