Injectable Dialer and Listener

[ggwpez]

Motivation: After using the payment library in a bot, we noticed that having an injectable Dialer and Listener would be good.

Goal: Add a way to inject a Dialer and Listener into the payment client.

Design:
Either:

1. Two new optional arguments to NewClient like payment.WithDialer and payment.WithListener
2. Two new functions SetDialer and SetListener on the Client object which can be called before Init