Improve Payjoin Notifications

[thibistaken]

When a payjoin succeeds, there is no obvious notification to help users understand it succeeded.

[BullishNode]

Closing as duplicate of #947. Payjoin notification improvements consolidated there.

[BullishNode]

Reopening - while related to #947, 'payjoin notifications' is a distinct request from 'payjoin status text improvements'. Apologies for the error.