Fixed #20003 -- Improved and extended URLValidator

Another attempt at fixing issue 20003, as it was previously attempted in #998.

This adds support for user:password in URLValidator supported URLs.

Additionally, the test suite has been improved by adding test URLs from
http://mathiasbynens.be/demo/url-regex (with a few adjustments, like
allowing local and reserved IPs).

The previous URL validation RegEx failed this test suite on 13
occasions, so I also updated the URLValidator based on
https://gist.github.com/dperini/729294 to correctly validate all URLs in
the test suite. Among other improvements, this also adds support for
IPv4 mapped IPv6 addresses like `::ffff:192.0.2.128` and support for
unicode domain names.

Docs have also been improved.
It wouldn't validate:
- http://.com
- http://.
- http://..
- http://../
- http://.www.foo.bar/
- http://.www.foo.bar./

It would indeed validate the following URL (but they are actually valid):
- http://example
- http://example.

All the others are about leading and trailing hyphens, if we really want to filter them out despite the increased complexity then I suggest we break the pattern into multiple variable for readability: https://gist.github.com/386830e46e8d2aca9dcb

Regarding formal grammar, it's spread out among a bunch of RFCs, I doubt it's worth the effort.