This is a conservative fix. If we wanted to really highlight the
feature graphic functionality and reward upstream devs for keeping
metadata up to date, then we could also take apps which were recently
updated, and prioritise them over new apps if they have a feature
graphic.
Fixes#938.
Also fixed display of feature graphic in main screen by getting full
path to image, not the relative path (e.g. "en-US/featureGraphic.png").
5b52835097