Some WriteFreely instances are completely private, and thus have no need for public-
oriented features like Web Monetization. Like federation, this gives admins control
over whether or not the feature is enabled for users.
Ref T773
This moves app config to a "Settings" page and the application monitor
to a "Monitor" page. It also reworks the admin navigation bar a bit and
adds some instance stats on the dashboard.
Ref T694