Show content under status bar

[wilsonpage]

Follow-up from #39

Currently the status-bar is dark grey and never shows any content underneath. When the content is scrolling it should scroll under the status bar to give a more 'full-screen' experience.

@gmarty is that correct or were you expecting the content should be under the status bar when scrollTop === 0?

[gmarty]

I think the content should be under the status bar all the time.
On Android I think the usual design is to have a slightly opaque (20%) dark background. But on iOS there isn't usually any background.
Because the app theme colours are quite dark we must also display the status bar icons in white.