WebSandboxMC

• Fix NPE in signs and log bad sign data (GH-92)
• Compile against SpigotAPI 1.12-R0.1

Update to NetCraft build 500:

• Change to disable local (client-side, non-server) terrain generation (satoshinm/NetCraft#189), only your web sandbox chunk will now be visible
• Change touch to use hold to mine, tap to place (satoshinm/NetCraft#186)
• Fix touch events missed on initial page load (satoshinm/NetCraft#193)
• Fix VR rendering support on WebGL platforms without draw buffers extension (satoshinm/NetCraft#89)
• Fix not using full window size for VR rendering and reinitializing when retoggled (satoshinm/NetCraft#183)
• Fix warnings by updating to glfw development version (satoshinm/NetCraft#190)
• Fix undefined behavior in unaligned memory load on client socket (satoshinm/NetCraft#192)

Test server http://netcraft.beerprojects.com has been updated to 1.12