Add Dropbox's zxcvbn library for realistic password strength estimation.

Upstream: https://github.com/lowe/zxcvbn. MIT License.
Modified for WordPress with a rot13 of the included word dictionaries, for PG-ness.

props duck_.
see #21737.

Built from https://develop.svn.wordpress.org/trunk@25156


git-svn-id: http://core.svn.wordpress.org/trunk@25135 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Use Dropbox's zxcvbn library for our password meter.

The library was added in [25156].

props duck_.
see #21737.

Built from https://develop.svn.wordpress.org/trunk@25157


git-svn-id: http://core.svn.wordpress.org/trunk@25136 1a063a9b-81f0-0310-95a4-ce76da25c4cd