Add an Emoji Typeahead

Summary:
This adds a more complete emoji datasource, with a typeahead and autocomplete. It works by pulling in a raw datasource from EmojiOne (I chose Unicode 8, but they have a Unicode 9 datasource as well) and transforming it for speed/need. If we build more robustness or an actual picker into the Remarkup bar, having the additional keywords, etc, might be important. When Unicode 9 support is more prevalent, we should only need to update the single file.

Tossing up as a proof of concept on engineering direction. Also I can't quite get the autocomplete to complete.

Test Plan: Test UIExamples, Autocomplete, and TypeaheadSource

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12139

Differential Revision: https://secure.phabricator.com/D17244