Log Message:
balsa: Update to 2.6.2

* Balsa-2.6.2 release. Release date 2020-12-21

- Webkit widgets are now sandboxed.
- Improved desktop notifications.
- iTIP calendar reply are improved.
- Handling of multiple crypto keys for the same recipient.
- build cleanups and improvements, e.g. application logging.
- code cleanups and simplifications as enabled by moving to more modern
  libraries.
- bug fixes: draft with message/external-body attachments;
  do not crash on importing half-broken keys
- improved translations.