Make screenHeight configurable

[violabg]

I'm trying to use this component in a tab view, so I have navigation bar on to has header and a footer with tabs. since you set the screenHeight of PhotoBrowser to the window.height, the height is too tall for the view where I'm rendering the component, and the images are not centred properly. You should make screenHeight configurable, or use its parent height and not window.height.

Thanks