Update to Emoji 16.0

[cocoelacanth]

This PR updates assets/unicode-emoji.json to include 36 new emojis added between Emoji 15.0 and 16.0.

This includes all emojis added in Emoji 15.1 and 16.0, with the exception of skin tone variants.

Additionally:

• The names and keywords for many existing emojis have been updated in accordance with CLDR v46.1.0
• Emojis no longer include their own name as a keyword; if this is problematic, it should be relatively easy to add them back
• Subcategory names now use hyphens instead of underscores; if this breaks things it should also be an easy fix

[cocoelacanth]

Apparently, renaming a branch closes any associated pull requests. Whoops