Show progress bar in propagate

[RemiLehe]

The propagate function can potentially take a long time (if the grid is large) ; this PR changes the code so that the propagate function shows the progress bar:

[hightower8083]

looks good to me, but one little question: could you check how this will look in methods with many propagations, e.g. gerchberg_saxton_algo. I'd imagine having many tens of dead bars might appear bit ugly, so an option to turn them off might be helpful.

[RemiLehe]

Ok, sounds good. I have made the progress bar optional and turned it off in the Gerschberg-Saxton function.

[hightower8083]

looks good!

[hightower8083]

.