iterative_ref: refactor to be more modular

[geoffwoollard]

• bayes weights --> lik weights: em refactor: wrap each em iteration #62
• remove griddata option in insert_slice, pad_and_rotate_xy_planes depedency: em refactor: wrap each em iteration #62
• type information in args
• generate_cartesian_grid primitive to coordinates module
• grid_SO3_uniform - a discretization of space transformation. in spaces