devel/py-twisted: Update to 20.3.0, Fix security vulnerabilities

Add extra_require dependencies as options, enabled by default.

Changelog: https://github.com/twisted/twisted/blob/twisted-20.3.0/NEWS.rst

PR: 245252
Exp-run by: antoine
Submitted by: contact@evilham.com
Submitted by: dereks_lifeofadishwasher.com
MFH: 2020Q2
Security: 9fbaefb3-837e-11ea-b5b4-641c67a117d8
Differential Revision: https://reviews.freebsd.org/D24186