Fix JSHint issues

 * Declare OldPreviewer var
 * Declare confirm() as global
 * use wp.ajax.settings.url instead of ajaxurl
 * ucfirst constructor var name
 * supply parseInt radix
 * Fix indentation to use tabs instead of spaces
 * Add use strict
 * Remove trailing commas from object literals
 * Use === instead of ==
 * Remove unused function args
 * Fix return value for getMenuItemPosition
 * Remove unused arr variable