Summary:
Ref T10054. Primary goal is to be able to remove IconNav from the codebase.
I've made these non-editable so users can't customize them yet. We //might// want administrators to customize these globally instead? In any case, we avoid a bunch of product questions by just locking these down for now.
Test Plan: {F1061348}
Reviewers: chad
Reviewed By: chad
Maniphest Tasks: T10054
Differential Revision: https://secure.phabricator.com/D15020
