Also removes a couple wrong Godot headers from third-party source files.
Consolidated duplicate snapping functions into CanvasItemEditor. Allow non-square grids. Add grid origin offsets. Allow seperate toggling of grid display. Add rotation snapping. Add offset snapping.
-Added Navigation & NavigationPolygon nodes -Added corresponding visual editor -New pathfinding algorithm is modern and fast! -Similar API to 3D Pathfinding (more coherent)