This functionality was never actually used AFAICT, as no way to provide
alternate profiles was ever provided.
This changes the configuration format to remove the `[global]` section,
everything that was previously under that namespace is now at the top
level.
The configuration file is now the canonical way to, well, configure.
This change is desirable because it gives us much more flexibility with
how configuration is structured. Environment variables are insufficient
because, for example, they're a flat namespace and have no built-in way
to represent lists.
This makes it possible to deploy Grapevine while using a database
originally created by Conduit, including leaving the admin bot user's
localpart the same as before.
