Merge pull request #458 from jrfnl/master

Make sure schedule_yoast_tracking is available for deactivation as well and has the correct file path.
Author sitemap logic is broken, props @jrfnl, fixes #464
Prevent saving "empty" values, as suggested in #463
Revert change to XML sitemap as it’s giving some issues and it’s no longer working.
Make `$bad_sitemap` public.
Change hook for sitemap redirect
Revert change to XSL stylesheet URL as that gives issues on WP Multisite installs
Bump to version 1.4.22.
Move shortcode function to functions file to make sure it is also available to posts which may be added to the site via ajax
Updated readme for fix