FPV Sim 1.2.1

Performance update.

• Big maps are split into areas so the parts behind the camera aren't drawn; frame times are the same or lower on every map.
• Much lower memory use (up to 533 MB before, now about 80–230 MB): map data is freed once it's on the graphics card, collision and water data are stored compactly, and only the last 2 maps you flew are kept in memory (1 on Android).
• Fewer small allocations while flying, for smoother frames.