Miscellaneous fixes for icon sizing issue, missing tree nodes to be

webpacked, etc.

- Fixed the background-size for the svg icons to 20x20 px such that it
  does not adjust it's size when a context menu height is different due
  to length of the node label, also - it allows us to fix the issue of
  icons sizes in the Grant Wizard.

- Added two missing browser tree nodes in the webpack configuration
  i.e. Foreign Server, and User Mapping
- Removed a redundant javascript file foreign-server.js
- Fixed the missing context menu icons for Foreign Table, and Tablespace
  nodes.

Thanks EDB development team to find the regression added after the icon
changes in quick time.

web/pgadmin/browser/server_groups/servers/tablespaces/static/js/tablespace.js

@@ -47,13 +47,13 @@ define('pgadmin.node.tablespace', [
           name: 'create_tablespace_on_coll', node: 'coll-tablespace', module: this,
           applies: ['object', 'context'], callback: 'show_obj_properties',
           category: 'create', priority: 4, label: gettext('Tablespace...'),
-          icon: 'wcTabIcon pg-icon-tablespace', data: {action: 'create'},
+          icon: 'wcTabIcon icon-tablespace', data: {action: 'create'},
           enable: 'can_create_tablespace'
         },{
           name: 'create_tablespace', node: 'tablespace', module: this,
           applies: ['object', 'context'], callback: 'show_obj_properties',
           category: 'create', priority: 4, label: gettext('Tablespace...'),
-          icon: 'wcTabIcon pg-icon-tablespace', data: {action: 'create'},
+          icon: 'wcTabIcon icon-tablespace', data: {action: 'create'},
           enable: 'can_create_tablespace'
         },{
           name: 'move_tablespace', node: 'tablespace', module: this,