Add religion icons to the city-states list

##sometimes i play with the papal primacy belief (50% to CS type bonuses for CS that follow your religion). It would be convenient to see the religion that CSs follow in the CS list rather than having to pan around the map or use the religion ui.
I'd be happy to contribute if anyone wants to coach me on how this could be implemented.

Start by locating the city-states list UI and the religion UI, then determine where each city-state's religion is available to the interface. Done means the city-states list visibly shows a religion icon for each applicable city-state, allowing the player to identify it without panning around the map.

Written by the indexing model from the issue text.