The customize routes add CSS classes that make these admin
config pages look different from the ones under /admin/config.
We want all config routes to be under /admin/config as well.
This commit moves the emoji, user fields, and permalinks pages
out of customize and into config, updating all references and
adding more rails routes as needed.
Also renames admin emojis route to emoji, emoji is singular and plural.
Setting tab should be added to permalinks so admins do not need to have left `/permalinks`.
A new component called `AreaSetting` was added to avoid duplications and
simplify adding settings to other sections.
