Fetch shortcut no longer honoured because of full-screen shortcut

The fetch shortcut used to be shift+cmd+F but the fullscreen has taken over it (it got auto-disabled when we created the fullscreen shortcut). Create a fetch shortcut which is instead alt+cmd+F. We can't use shift+cmd+F because fullscreen adheres to Apple UI standards.

Reported via AAC here: https://answers.atlassian.com/questions/172296/why-did-you-guys-remove-the-command-shift-f-shortcut-to-fetch