Replace custom code with has_shortcode()

git-svn-id: https://plugins.svn.wordpress.org/basic-google-maps-placemarks/trunk@898365 b8457f37-d9ea-0310-8a92-e5e31aec5664
Extract marker cluster style options into separate function

git-svn-id: https://plugins.svn.wordpress.org/basic-google-maps-placemarks/trunk@898366 b8457f37-d9ea-0310-8a92-e5e31aec5664