[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/spec/javascripts/sqllab/fixtures.js

@@ -250,7 +250,6 @@ export const queries = [
 
 export const initialState = {
   alerts: [],
-  networkOn: true,
   queries: {},
   databases: {},
   queryEditors: [defaultQueryEditor],