optionally allow admin users to login to user servers by visiting a special admin-only URL that sets the relevant cookie
- disabled by default
- an 'access server' button is added to the admin panel, which sets the necessary cookie to log in to the user server
such as VMs, batch and cloud services, etc. which can take minutes to start.
- Spawner.start_timeout sets a limit for true failure,
at which point spawner should be considered dead.
- Handler.spawn_single_user only waits up to 10 seconds
before returning. It can now return with a spawner still pending.
- Record User.spawn_pending state, and render 'pending' page
while server is starting but not started.
Allow authenticators to:
- register custom handlers
- change login and logout URLs
- replace the entire login form
This appears to be enough to get oauth working.
- index no longer requires login, it's just a big fat login button
- home has stop, start, admin buttons
- admin doesn't do anything yet
- add jhapi javascript client for REST API