Fix for Bug#4237 

In continuation with [Pull Request#893](https://github.com/phpmyadmin/phpmyadmin/pull/893)...

Whitelist check for domains in url.php has been added. I've tried to add as many valid domains into the [Whitelist](https://github.com/dhananjay92/phpmyadmin/blob/54813d8ddd34e3362ca64e3c56f67c2a4ca6064a/libraries/core.lib.php#L828) as I could. <b>Please point out if any domains have been missed.</b>

Travis-CI build fails because, it is comparing the new results with some old result which has token in all its outgoing URLs, and so string comparisons fails on those URLs.  See [build log](https://travis-ci.org/dhananjay92/phpmyadmin/jobs/18323350).