The goal of this rework is to make it so I can pass around platform.User
instead of a pair of models.Organization and models.User. This is useful
for reason I kind of forget now, but it started with working on
notifications and ballooned massively from there into refactoring a
number of things that were bugging me.
This also includes a tiny amount of work on server-side events (SSE).
* background stuff lives inside the platform now, which I need for
having it push updates through SSE
* userfile now lives in the platform, under file, so other platform
functions can safely use it
* oauth is broken into pieces and inside platform because other stuff
was calling it already, but badly.
* notifications go into the platform as well
