-PGN text is not selectable (understand why?!)
-Checkered stage 2: switch button at reserve position (or on top).
-Mode expert: game.js, button on top (with online indicator)
-Turn indicator on top too (black or white)
+Finish showProblem() in components/problemSummary.js (send event with infos, and pass message to game component)
+Add new mode in game component: "problem", in which we show description + hidden solution (reveal on click)