The default export here replaces Expo's <Iconicons/>, <Fontawesome/>,
etc. components with <Icon/> in a first step away from the Expo
ecosystem.
Using PNG images greatly limits our access to unique colours, but since
there only should realistically be using two colours, #000 and #666, in
the interface, hopefully this won't be a problem. At least not until
there's a dark theme. Rendering more PNGs from the SVGs is tedious.
