Secure Cookie Versions Save

https://secure-cookie.readthedocs.io/en/latest/changes/#version-0-2-0

Changes:

• Extracted from Werkzeug 0.15.
• Dropped support for Python 3.4.
• SessionMiddleware sets secure_cookie.session in the environ instead of werkzeug.session.
• FilesystemSessionStore uses the filename template secure_cookie_%s.session instead of werkzeug_%s.sess.
• SecureCookie.serialization_method is json instead of pickle. To upgrade existing tokens, override unquote to try pickle if json fails.