Change frameRadius to use pen widths, add frameRadiusForNewPenWidth, add PenWidth::NoPen

Summary: This patch reduces the amount of duplicate code and makes every part of the helper functions use the correct frame radius.

Reviewers: Breeze, Plasma, hpereiradacosta, ngraham

Reviewed By: hpereiradacosta

Subscribers: plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D26225