Summary:
Adds tests to the emoji picker.
The emoji picker should also now be able to add emojis consecutively (without spaces).
Finally, the toolbar positioning bug (emoji picker appearing in front of typed text, the toolbar manager appearing in the upper left corner when empty lines are selected) should be fixed so that the toolbar appears directly above/below the selection area.
Test Plan: Tests included in diff.
Reviewers: evan, bengotow
Reviewed By: bengotow
Differential Revision: https://phab.nylas.com/D2551
