[Feature] Update to Pyramid 2.0

[fmigneault]

Update of Pyramid 2.x deprecates Authentication/Authorization policies in favour of a combined Security policy.
This breaks Magpie completely, which is why it is pined with pyramid < 2.

Considering update to follow the new policy implementation will require some changes as decribded in:
https://docs.pylonsproject.org/projects/pyramid/en/latest/whatsnew-2.0.html#upgrading-authentication-authorization

At some point, upgrade might be needed to receive any future improvements or security updates.
Some performance improvements are also added, such as https://docs.pylonsproject.org/projects/pyramid/en/latest/api/request.html#pyramid.request.RequestLocalCache, to cache expensive operations during the lifetime of a request.