Ensure unicode slugs work everywhere #315

Starting with d187567, our slugs (for organizations/accounts/documents) can contain alphanumerics from any language (\p{Letter}\p{Number}).

This works within the platform, but we need to verify and repair (if necessary):

• Embeds (including oEmbed)
• External patterns (like here and here) that bake in our old slug format
• validator.js
• S3/CloudFront

References:

• http://www.regular-expressions.info/unicode.html
• http://stackoverflow.com/questions/280712/javascript-unicode-regexes
• https://mathiasbynens.be/notes/javascript-unicode
• https://mathiasbynens.be/notes/es6-unicode-regex