v3.1.1

This is a bugfix release that fixes a bug introduced in 3.1.0. The bug leaves the amount field editable on desktop clients and crashes mobile clients when clicking a payment link or scanning a payment QR code. Now the bug is fixed.

SHA256 hash of the linux AppImage is bebf1a1fb540bcbc941d6efbc4be913f4ba82c71ccfe9b02eca26d5f02f30231, binaries for other platforms are already signed in ways that are standard on the respective platforms.