Batch Payments to Lightning Address

[pretyflaco]

Background
The batch payments beta allows users to send batch payments to multiple Blink usernames. Sending batch payments to Lightning Addresses of external wallets is not supported.

Motivation
Multiple NGOs in Africa are using this feature to dispatch payments to their project members. One NGO reached out stating that 50% of their project members have phones that do not support Blink. Those project members are using Machankura, which works on low-end devices and feature phones. Payments to these project members currently need to be done individually via send to Lightning Address in Blink mobile app.

Adding support for payments to external Lightning Addresses to Blink batch payments would help streamline the payment process by allowing payer to pay to external Lightning Address in addition to Blink users.