Manage main page scroll position

[alistairjcbrown]

Currently we have a bit of a hack where we save the a flag on whether the back should be browser vs Nextjs link.

But, if the user navigates between pages (like between a multi movie -> single listing, and then clicks the "Back to film list", we can't go back -- so the list position is reset.

What if instead we saved the scoll position into state, and use it the next time we land back on the poster page?