Fix scrolling behaviour

[Nick]

If we want the app to feel more solid, we should / can prevent scrolling when the app is fully viewable in the phone window, i.e. when you pull down or push up, the app doesn't move like a website. There is a nice way to do this with fixed css positioning, it will take a bit of hacking.

This makes it feel more solid, like it can't be pulled or pushed when it shouldn't be.