Before this pr:
Discover, Visualise and Dashboard in setup phase create own state containers which watch for pinned filters, time and refresh interval changes. This watching and state comparisons happen for each plugin separately and not only when a specific app is mounted. So we ended up with a bunch of similar synchronous work which happens every time query services state changes.
After this pr:
Query service exposes observable to watch for changes (state$). Discover, Visualise and Dashboard use this observable for sub url tracking instead of creating its own.
Today, apps rely on AppState and GlobalState in the ui/state_management module to deal with internal (app) and shared (global) state. These classes give apps an ability to read/write state, when is then synced to the URL as well as sessionStorage. They also react to changes in the URL and automatically update state & emit events when changes occur.
This PR introduces new state synching utilities, which together with state containers src/plugins/kibana_utils/public/state_containers will be a replacement for AppState and GlobalState in New Platform.
