mem_limit & cpu_limit are traitlets on the parent
Spawner class. Setting these here allows plugins to
do the dangerous job of swapping the SystemdSpawner
out for something else
No two ways to set authenticator options - just one way.
It's slightly 'ugly' because of the mixing of camel case &
snake case, but is worth the massive reductions in complexity!
- Removes all need for special casing authenticators.
- Install them in hub environment, directly start using them.
- Consider if we should special case any *at all*
