Time-based expiration of ID store keys (#89)

- Allows actual Forward Secrecy, as keys of messages read or skipped now expire after 10 minutes.
- Due to lacking agent implementation, expiration only occurs when ID store is used by running Covert.

GUI improvements (#68)

* Refactor to use QMainWindows.
* Implement flash status messages.
* GUI separation into independent views, a new look and minor UX improvements.
* Implement attached file extraction on decryption. More refactoring.
* More fixes related to refactoring. Usability improvements.
* Auth/signature info on decryption.

Co-authored-by: foonoxous <RWQe4qDs7LIsmI7Q94ctNMSfwfDW8eld24YGevEzQEKZyfJz1NPlH6uf>

Avoid crash on Python 3.9.2

Updates the requirement of zxcvbn-covert to 5.0.1 which contains additional fixes, most importantly a workaround to a bug in Python that was preventing the program from running.

Additional e2e test on CLI for more coverage (#52)

* Additional e2e test on CLI for more coverage.

* Verify signatures

Co-authored-by: foonoxous <RWQe4qDs7LIsmI7Q94ctNMSfwfDW8eld24YGevEzQEKZyfJz1NPlH6uf>

Run a full encryption/decryption cycle over CLI (#49)

Co-authored-by: foonoxous <RWQe4qDs7LIsmI7Q94ctNMSfwfDW8eld24YGevEzQEKZyfJz1NPlH6uf>

Trying another email to satisfy PyPi.

Depend on our own fork of zxcvbn on PyPi.

Update hashing not to use the header, as it is included as AAD on Blo…

…ck0 which always gets verified.

Try MiniSign keys with an empty password first.

Merge pull request #16 from ahopkins/patch-1

Add missing requirement: pysodium