Unreadable pilot files should be visible, but not selectable

Within the initial player selection lobby and the barracks, pilot files that can't be read by FSO (due to missing required data) should still be visible to the user, but not selectable. This is so that players know at least that the pilot is still there without needing to navigate to the `/players` directory. The UI should also inform with a popup when it detects unreadable pilots.