graphics/py-mcomix: Update 2.2.1 => 3.1.1

Changelogs:
https://sourceforge.net/p/mcomix/git/ci/3.1.1/tree/ChangeLog.md

While here fix warnings from portclippy and replace PORTVERSION with
DISTVERSION in MASTER_SITES.

PR: 289478
Approved by: Stefan Ehmann <shoesoft@gmx.net>