v1.2.2: maintenance release that works with Inbox

This release is for all those out there who want to stick with Inbox until the bitter end.
In an attempt to alleviate a very confusing situation, it displays a dialog on startup that informs the user about the current situation with Inbox and which versions of Inboxer will continue working with Inbox and which have been migrated to use regular Gmail.

Highlights:

• Display dialog on startup explaining Google's decision to kill Inbox
• Notify about Snoozed messages
• Notify on file download
• Add notification preferences