Dashboard: simplify interactions between AppState, Global State, URL and Redux State

[stacey-gammon]

This is a common source of bugs. Historically, when dashboard was written all in angular, it used AppState and the URL to handle state updates. When we started transitioning to redux and react, dashboard was one of the first to make the move.

"dashboard_state_manager" was created to bridge the gap between Redux state, and the URL which is managed by AppState and GlobalState objects.

Goal

Remove dependency on AppState and GlobalState objects letting redux handle syncing the URL.

Pre Req TODOs

• Investigate best ways to handle URL syncing in the redux world. Do we introduce react-redux-router, react-router or try to do something manually? Note: APM did some work here, would be worthwhile to sync with them.
• Investigate how the interaction will work if embeddables modify core components, like the time picker, directly. Does the flow go embeddable -> time picker -> url -> react router? I think listening to URL changes should be sufficient, but it will require some digging to be sure.