Change primary monochrome icon colors to match new HIG colors

Summary:
The old colors were Icon Grey (#4d4d4d, breeze) and an undocumented white color (#f2f2f2, breeze-dark). The new colors are Shade Black (#232629, breeze) and Cardboard Grey (#eff0f1, breeze-dark).

With this change, icons in GTK applications will be the same color as icons in Qt applications with the Breeze and Breeze Dark colorschemes.

I used sed --follow-symlinks -i 's/4d4d4d/232629/' *.svg for breeze and sed --follow-symlinks -i 's/f2f2f2/eff0f1/' *.svg for breeze-dark in each directory containing monochrome icons, excluding the color icons in apps/16 and apps/22

Test Plan: I'm unsure how to prove that everything is as it should be with such a massive amount of small changes, but I did look through the diff for every file in git-dag and found no mistakes.

Reviewers: VDG, Breeze, ngraham

Reviewed By: VDG, Breeze, ngraham

Subscribers: ngraham, andreask, kde-frameworks-devel, Breeze, VDG

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D17033