Article viewer: Use default profile so the font settings actually work

Summary: Font settings minimum, medium, etc were never used because they were applied to a different QWebEngineProfile than the one used.

Reviewers: knauss

Reviewed By: knauss

Subscribers: knauss, #kde_pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D12407