Add some watchtower support

[kristapsk]

As Nakamochi is device people run at home, with no 24x7 uptime guarantees, some support for watchtowers should be added, so that risk of LN channel counterparty stealing funds is reduced. For the start, some free altruistic watchtowers could be added by default. In future, qeles could run it's own watchtower.

https://raspibolt.org/guide/lightning/lightning-client.html#adding-watchtowers