Allow hiding non installed macros

Admins are now allowed to hide macros suggested in the "Add macro" feature in CKEditor. This was implemented at XWIKI-19993.

This feature has a "Not installed" category and the new configuration option does not take this in account IIUC.

See xwiki-platform/xwiki-platform-core/xwiki-platform-ckeditor/xwiki-platform-ckeditor-ui/src/main/resources/CKEditor/MacroService.xml

It would be nice to have a way to disable the "Not installed" extensions, through this new option or another one.

Workaround:

li[data-macrocategories="_notinstalled"] {
  /*Workaround for https://jira.xwiki.org/browse/CKEDITOR-509 */
  display: none;
}