Ent-eigen editors/calligra.

The recent update of math/eigen3 broke editors/calligra, as opencv and eigen-3.2+ contain same named parts.
Remove the using namespace Eigen from the files, and import the qualified class names instead.

This is a simplified backport of https://phabricator.kde.org/R37:2db4438671e17002c7b02e3ad3a5208930765e4f .

Reviewed by: rakuco
Differential Revision: https://reviews.freebsd.org/D11243