OpenPGP applet GNOME Shell extension: dynamically update the icon & menu depending on the content of the clipboard
_Originally created by @intrigeri on [#11936 (Redmine)](https://public-redmine-archive.tails.boum.org/code/issues/11936)_
Feature Branch: alan/openpgp-applet:feature/8310-gnome-shell
### Attachments
* [testDBusService.py](https://redmine.tails.boum.org/code/attachments/download/1497/testDBusService.py)
Parent Task: tails/tails#8310
### Related issues
- [ ] **Blocked by** tails/tails#11934
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