Configure the crop image with a variable size

There is now an option to change the size of the image used when
cropping. So whichever is smaller, your image or 600 px will be used
when displaying the crop image.
Refactor main and start 2.0.2-beta
Crop Constraints shown in GUI
2.0.1
Configure crop size & give crop size feedback

The crop picture can now be changed in the main crop settings on a
per-user basis.

The crop feedback works by alerting the user when a crop will
potentially have a less than 1:1 crop by turning red. (Green when better
than 1:1)