Summary:
This shows a changelog as popup at startup, but only if it wasn't shown before, and only if there are new items in the changelog.
The full changelog can still be accessed through the menu
Changelog: From this release onward we will show important update messages through this dialog.
Reviewed By: passy
Differential Revision: D20492594
fbshipit-source-id: 4663979c8781b468430b9f8b628c4f506578b461
805a911c08