#43 Crop filter improvements - make cropped selection draggable and add grid

[InStars]

Often when cropping you need to fine tune the crop to center the video to some object while maintaining the size and aspect ratio. It would be really useful to be able to move the crop by dragging it while retaining the size of the crop. And an option with large square grid (like 3x3) could help us to better center our crops.