Add highlights to clicked polities

[edwardchalstrey1]

• [x] Make it so clicking a polity increases the border weight so it is highlighted
  • Make highlight disappears when you click on a different polity (perhaps don't want this anyway?)
• [x] Ensure highlight persists when year changed
• [x] Ensure highlight persists when view switches to all polities or just disable this feature until all polities loaded
• [x] Add polity to legend when clicked
  • Maybe a minus button to remove it from the legend just click away
  • [x] Remove polity from legend when it's not still there
• [x] Remove polity from legend when you click it again