Explore: Use PanelQueryState to handle querying (#18694)

* WIP: inital POC

* Wip: Moving forward

* Wip

* Refactor: Makes loading indicator work for Prometheus

* Refactor: Reverts prom observable queries because they did not work for multiple targets

* Refactor: Transforms all epics into thunks

* Fix: Fixes scanning

* Fix: Fixes so that Instant and TimeSeries Prom query loads in parallel

* Fix: Fixes negation logic error

* Propagate errors in stream events, and close streams

package.json

@@ -230,7 +230,6 @@
     "react-window": "1.7.1",
     "redux": "4.0.1",
     "redux-logger": "3.0.6",
-    "redux-observable": "1.1.0",
     "redux-thunk": "2.3.0",
     "reselect": "4.0.0",
     "rst2html": "github:thoward/rst2html#990cb89",