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