Fetch origin periodically

[Eonfge]

It would be nice you could configure a periodic fetch per origin. This will help you stay up-to-date with other developers without having to switch to another application.

Proposal

• In the Edit Remote screen, there is another checkbox refresh periodically that tells GitFourchette to fetch the remote every x minutes.
• In the Settings -> Advanced screen, a user can configure a custom refresh interval in minutes