Check that padding, spacing, etc. work with inequal step over dimentions

[KonstantinUshenin]

• math_core.py, grid_in_cube, spacing
• math_core.py, grid_in_cube2, spacing
• math_core.py, scale_xyz, scale
• math_core.py, scale_xyz, scale
• datagen.py, DataGenForSegmentation, cube_spacing
• datagen.py, DataGenForShapeRegression, spacing
• datagen.py, _scale_rotate_shift, scale
• method_set.py, SamplingMethodSetNode, sampling_grid, spacing
• sampling_grid_with_noise.py, SamplingMethodSetNode, sampling_grid, spacing
• sampling_grid_with_noise.py, SDTMethodSetNode, surface_xyz2localsdt, spacing
• method_set_train_task.py, TrainTaskSetNode, train_task_sdt2sdf, spacing
• space.py, Space, preload, ps_padding, ns_padding
• abstract.py, AbstractBBoxNode, plot
• vizualize.py, save_3D_slices
• vizualize.py, save_sdt_as_obj
• vizualize.py, save_mesh
• vizualize.py, save_3D_array

[semyon-v-dot]

I'm going to test math_core.py