[0.6.x + 0.7.0 pre2] Nomad Physics

First release: rigid bodies, terrain and model-shape collision, joints, the physgun and the gravity gun, with PhysicsApi available to other plugins. Includes a placeable crate and bricks in eight colours, all with inventory icons. Packs can register machines as placeable items through PhysicsApi.registerMachine: look at a block to place one, then sneak + F to pick it up. Per-world tile and speed budgets limit the load from pile-ups. Diagnostic logging is off unless Diagnostics is enabled in config.