Feature/6299 new doc

* New doc struct for encryption keys https://leap.se/code/issues/6299
* Multi uid support https://leap.se/code/issues/6212
* Keep old key after upgrade https://leap.se/code/issues/6262

Do we miss a "raise" here? And if we raise, what happens with the key we're trying to delete? Will it remain in the keymanager forever just because it has more than one key fr that key_id?