implement coarse position correction

[yijiang1]

Currently the best way to correct large position errors in ptychography is to do low-resolution reconstruction using cropped data. However, sometimes reconstruction may fail if diffraction patterns are too small, preventing position correction at large pixel size. I think it's possible to do coarse (or any arbitrary pixel size) during the position correction step by resizing the object and the probe. Thus one can use large diffraction patterns and still perform efficient position correction.

[yijiang1]

Perpahs all we need is to add a resizing step in /+GPU/private/gradient_position_solver.m