Summary: The emoji picker allows users to insert emoji to their messages on click. A few emoji that don't render properly in Chromium are replaced with PNGs, both in the composer view and the message list view, but only the Unicode characters are sent in the message bodies.
Test Plan: TODO
Reviewers: bengotow, evan
Reviewed By: evan
Differential Revision: https://phab.nylas.com/D2787
