Add App description and author to app store

[Jonty]

Currently when browsing the app store selecting an app immediately installs it, we should instead show a screen with the app description, author, and version, and an option to install it.

We may need to make the description auto-scroll or something?

[andypiper]

Currently you can press B to get the description (and DOWN to scroll that, but it never re-centres for the next one), but yeah I think adding all of this would be helpful. Maybe small icons by each button to indicate info and install.