Big UI commit - GUINode, MaskedFlag, PieChart, etc

[Hop311]

• Updated sim submodule to include a lot of recent work (and some bug fixes, e.g. the MSVC v19.38 lexy bug)
• Added GFXMaskedFlagTexture and GFXPieChartTexture
• Added GUINode to handle generating and controlling UI defined in .gui and .gfx files (UIAdapter still does the actual generation, GUINode just provides the GDScript/godot-cpp interface)
• Changed ProvinceOverviewPanel and Topbar to use GUINode, removing old GameSpeedPanel
• Fixed some issues with the LoadingScreen thread (trying to wait for itself to finish)
• Added lots of functionality to the ProvinceOverviewPanel, including:
  • Proper pop icons for slave state, admin efficiency and owner %age
  • Terrain image updates with terrain type
  • working pie charts for pop type, ideology and culture (ideology doesn't show anything because it's not generated in the SIM, but the pipeline from there to the UI works)
  • Crime icon and name reflects province's crime modifier
  • liferating bar fixed
  • colony status accurately shown (although only at province level, needs more state work to be shown in all provinces in a state)
  • controller country flag icon
  • loads of other labels, some with placeholder text, others with correct data
• Added dedicated script for Topbar, including player flag and name control and working date and speed/pause buttons