Python 3.12 and assorted fixes

[bryango]

This PR makes the app work for python 3.12. It incorporates the fix from https://github.com/pulb/mailnag/issues/245#issuecomment-1753068005. Closes:

• [x] #244
• [x] #245

Some other improvements:

Fix SSLV3_ALERT_HANDSHAKE_FAILURE for some imap servers

Connections to some imap servers (e.g. imap.pku.edu.cn) fail after upgrading to python 3.10. This is because they use old, less secure ciphers that are disabled for Python 3.10. In order to connect to those servers, we have to allow more ssl ciphers in imaplib2 for Python 3.10. See:

1. https://stackoverflow.com/a/71007463
2. https://www.openssl.org/docs/manmaster/man1/openssl-ciphers.html#CIPHER-LIST-FORMAT

Also,

• Exit gracefully when autostart creation fails
• Use raw strings for backlashes