v2.0.0

• Ported to Python3
• Migrated from Gnome keyring to libsecret
• Moved functionality of dbus plugin to mailnag core
• Added support for CRAM-MD5 auth
• Added STARTTLS support for pop3 accounts
• Cosmetic UI fixes
• Misc other fixes and improvements

IMPORTANT NOTES FOR PACKAGERS:
Please note that mailnag now requires python >= 3.5 and
that the GNOME-Keyring dependency has been replaced by libsecret.