Add 'Visit Dashboard' and 'Edit Site' links to the site added message on...

Add 'Visit Dashboard' and 'Edit Site' links to the site added message on site-new.php. props vegasgeek, SergeyBiryukov. fixes #18047. fixes #17313.

git-svn-id: https://core.svn.wordpress.org/trunk@18750 1a063a9b-81f0-0310-95a4-ce76da25c4cd