Add window.restoreZenMode option

[yogaraptor]

I'd like code to open in Zen mode so I'm distraction-free immediately. There's already a window.restoreFullscreen which does the equivalent for fullscreen mode, but it would be great to be able to go that one step further and "boot up" in zen mode.

[mousetraps]

Nice idea! cc @isidorn

[isidorn]

I have added zenMode.restore. Feedback on the name is welcome
Alternative was zenMode.restoreOnStart

@bpasero maybe you have an idea for a better name

[bpasero]

Thats ok, we have window.restoreFullscreen for the fullscreen state.

[yogaraptor]

I assumed it would be window.restoreZenMode but I really don't mind as long as it's there ;)

[isidorn]

All zenMode settings are under zenMode.

[jrieken]

This isn't working for me on Linux/Mac with latest Insiders

[isidorn]

Fixed in latest, there was an issue which @sandy081 uncovered. Will be in tomorrows build