Mounted sub-apps should hook into their parents setup

[daffl]

Initially brought up in feathersjs-ecosystem/authentication#72, sub-apps will hook into their parent setup (so that you don't have to call a sub-apps setup manually) only when a real-time provider is configured. This should however always be the case.

Since it may cause odd errors (with app.setup being run twice) the best way is probably to change this in v3.

[sdbondi]

Hi @daffl Could you please update the docs to reflect the need to call setup() on sub apps? Specifically: http://docs.feathersjs.com/middleware/routing.html - Thanks 😄

EDIT: Ah I see it is mentioned here: http://docs.feathersjs.com/middleware/mounting.html#sub-apps