Same Client ID can be used by server-side and on-device components of the client

[elf-pavlik]

This comes out of https://github.com/solid/notifications/issues/35

Even if this doesn't affect spec we should probably show how it can be done in the primer. For the End-user it should be transparent that the client has two separate components. I think both of them using the same Client ID should be sufficient. If both components share the refresh token, issues may come up around rotating them. I think one of the components would be responsible for refreshing tokens and the other component would just get current access token from it.