Infrastructure and changes to the Query Tool for realtime preference handling. Refs #3294

Highlights of this patch include:
- Changes will affect SQL Editors in Create dialog boxes, SQL tab of the main screen, Query tool, History entries in the query tool, Query tool opened in New Tab/Window
- All the components of SQL editor will refer to single source of preferences which is cached in the Browser object. All other redundant ajax get preference calls are removed.
- SQL editor will not refer template JS variables anymore, once all the references are removed the template variables will also be removed.
- Code refactoring wherever possible.
- Covered JS test cases wherever possible.

web/webpack.test.config.js

@@ -83,6 +83,7 @@ module.exports = {
       'pgadmin.backform': sourcesDir + '/js/backform.pgadmin',
       'pgbrowser': path.resolve(__dirname, 'regression/javascript/fake_browser'),
       'pgadmin.schema.dir': path.resolve(__dirname, 'pgadmin/browser/server_groups/servers/databases/schemas/static/js'),
+      'pgadmin.browser.preferences': path.join(__dirname, './pgadmin/browser/static/js/preferences'),
     },
   },
 };