Summary:
- Updates support for ES6 code inside packages
- Displays system tray icon with unread count on darwin, or with bubble on other platforms
- Uses canvas api to dynamically generate icon image given unread count:
- Adds CavasUtils.canvasFromImgAndText to do this
- Adds config option to display system tray icon on darwin
Test Plan: Need to write the tests for this.
Reviewers: evan, bengotow
Reviewed By: bengotow
Differential Revision: https://phab.nylas.com/D2231
