Add a 3D axis to the 3D view.

...visualization/controllers/loadables/meshes/base/Mesh.java

...lization/controllers/loadables/meshes/base/Primitive.java

.../controllers/loadables/meshes/extended/AxisPrimitive.java

...alization/controllers/loadables/shaders/SimpleShader.java

...apvox/visualization/controllers/voxels/SimpleProgram.java

...lidar/amapvox/visualization/controllers/voxels/Space.java

...alization/src/main/resources/shaders/simple/fragment.glsl

...sualization/src/main/resources/shaders/simple/vertex.glsl