Obfuscate an area

As a user with the "Obfuscate" permission on the document, I can obfuscate an area while in regular mode.

Acceptance criteria:

The action to obfuscate an area is only available while in regular mode. I can use it to select any area (e.g. in an image) and obfuscate it. The action behaves as a "highlight rectangle" annotation with black color and 100% opacity. I can't edit the annotation properties.