Improvements for Updater

[AliveDevil]

Allow updates to be scheduled on application exit, in addition to now, later and skip.

https://corteximplant.com/@kaiserkiwi/110032112658090769

[AliveDevil]

When I start Cyberduck, I have a task in mind I want to accomplish. The regularly appearing update request chafes me.

I would appreciate a "download new version in the background & install it when I quit Cyberduck" option.

#14535 (comment) by @Teetrinker