Toggle-option: if the next/prev day doesn't exist, create it

[isosphere]

I just hit the "next" button, hoping to go to tomorrow's journal. That page did not exist yet and so the button push did not do anything. I think I might like it to just make the page if that happens again, but I want this to be non-default behaviour locked behind an boolean user setting.

Creating "prev" might hypothetically be nice for someone, but you could also end up with a lot of blank journals after mashing the button for while. 🤷‍♂️ easy enough to lock behind a setting.