Inconsistent documentation for classes with .from_image_properties class method

[iancze]

Describe the bug
The documentation for several routines is inconsistent between the __init__ and from_image_properties calls. Some document coords. Many from_image_properties calls are undocumented.

• mpol.gridding.DirtyImager
• mpol.gridding.DataAverager
• mpol.fourier.NuFFT
• possibly others

Suggested fix
Document the from_image_properties and check the __init__ call is consistent with the remaining arguments.

Or, remove the from_image_properties calls entirely. Is this a feature we actually use? I find more often than not that it is more concise to instantiate a GridCoords object and then pass that to routines needed.