Make the New Version notification dialog non-modal or less obtrusive.

### What
(Windows version 2.8.0)
On each launch the app is checking for the new version and shows modal dialog box, announcing a new version (e.g. New Version 2.9.0 is available, your version is 2.8.0).

Please make this dialog box non-modal.
_- - or - -_
Please make the notification of the new version during application exit, not during application launch.

### Why
The modal dialog box disrupts user's workflow, forcing to take an immediate action (e.g cancel or upgrade).
There are some situations where the user (i.e. me) would like to defer the update to a later point of time.

Please consider my usual workflow scenario:
1) I'm opening the Simplenote app to get some reference information.
2) The popup box prevents me from using the app.
3) I cancel the new version box, because my immediate priority (the working context) is to get some reference data from a note.
4) Now that the box is cancelled, I can get the data from the note and continue with the workflow.
5) Five minutes later I close simplenote app, because now I'm cleaning up my working context.
6) I FORGET about the simplenote notification about the new version.
I should have checked and applied the new version, but there is no reminder anymore.
Because of the time gap and context switches, I'm not aware of the update anymore.
7) Goto 1

No source files, tests, or entry points are named. Trace the new-version notification flow for application launch and exit, then verify that the update notice no longer blocks normal use and remains available for users who defer the update.

Written by the indexing model from the issue text.