backendUrl vs __BACKEND_URL__ clarification

[veeramarni]

Noticed that you have backendUrl mentioned twice in the README.md and in the code.

Based on my understanding from the Doc, it was encouraged to use __BACKEND_URL__. If that is the case then I have noticed some discrepancy as __BACKEND_URL__ won't help in SSR. So to clarify we still need to use backendUrl for changing the default URL. And __BACKEND_URL__ will be defined automatically by spinjs based on backendUrl. This is what used to be, so wondering if that was changed as I noticed it was defined explicitly in here https://github.com/sysgears/apollo-universal-starter-kit/blob/master/packages/server/.spinrc.js#L9

[larixer]

@veeramarni backendUrl is still supported for backwards compatibility, but it is encouraged to set defines explicitly in defines section and to wait for backend to start now it is possible to use separate option waitOn:
waitOn: ['tcp:localhost:8080']

defines + waitOn completely replace backendUrl and are more explicit