Add staged resampling fitting to speed up fits

[Tom Dimiduk]

Calculating holograms for fits takes a long time, especially if the are at all large. If we resample down and calculate for a smaller hologram a fit will finish much faster, we can use that as a (hopefully very good) initial guess for a higher pixel number higher resolution fit. This process might take less time than fitting from the start with a large pixel count image.

[Vinothan N. Manoharan (vnm)]

I'm going to target this to 2.0 because we've made some progress already, and it's an often-requested feature.

[Tom Dimiduk (tdimiduk)]

use_random_fraction gets most of the benefits of this. How important does this stay once we have the random fraction calculation/fits?

[Tom Dimiduk (tdimiduk)]

I am marking this opinion, random subset fitting should replace it. Feel free to reopen if you come up with a use for it.