Settings UI tweaks

[chucker]

• [ ] Consistent width (Notifications is currently wider)
• [ ] Change title to Settings, at least when on Ventura (menu item is already auto-changed)
• [ ] Change toolbar icons to be monochrome glyphs (as in e.g. Finder, Safari)
• [ ] There seem to be a few cut off pixels at the top of the toolbar icons (probably a Big Sur thing)
• [ ] Animate tab switch (Finder and Safari do; Music does not)

[chucker]

We should also consider what to do about settings that aren't available in High Sierra (see #126). For example, by migrating to stack views…