Cookie-manager

Fix issues with the upcoming itsdangerous release [2.0.0rc1](https://github.com/pallets/itsdangerous/releases/tag/2.0.0rc1)

This release fixes a security vulnerability discovered and patched in a dependency.

See Bleach [3.3.0](https://github.com/mozilla/bleach/releases/tag/v3.3.0) for further details.

This release introduces the new `CookieSecurityDecorator` class.

It allows the cookie manager to protect functions via decorators.

- Bumped Bleach to patch another vulnerability
- More defensive logic around verification with unknown keys

Bumped up dependency versions to fix a security issue (thanks Dependabot!)

Fixed bug in packaging surrounding imports.