[sql-lab] performance updates - make ui more responsive (#2469)

* remove network status feature

* only fetch queries if there are started or running queries

* don't use local storage

* remove last network status from actions

* don't remove support for local storage

* address pr comments and linting

* use .some rather than .forEach

superset/assets/javascripts/SqlLab/reducers.js

@@ -17,7 +17,6 @@ export function getInitialState(defaultDbId) {
 
   return {
     alerts: [],
-    networkOn: true,
     queries: {},
     databases: {},
     queryEditors: [defaultQueryEditor],
@@ -230,12 +229,6 @@ export const sqlLabReducer = function (state, action) {
     [actions.REMOVE_ALERT]() {
       return removeFromArr(state, 'alerts', action.alert);
     },
-    [actions.SET_NETWORK_STATUS]() {
-      if (state.networkOn !== action.networkOn) {
-        return Object.assign({}, state, { networkOn: action.networkOn });
-      }
-      return state;
-    },
     [actions.REFRESH_QUERIES]() {
       let newQueries = Object.assign({}, state.queries);
       // Fetch the updates to the queries present in the store.