Image cropping and rotation

[ApoorvaJ]

I am currently working on a common tool to handle cropping and rotation.

At least for now, cropping/rotation operations will be destructive once confirmed, meaning you will not get the cropped area back without using undo.

I'm working on this in the crop_and_rotate branch, and posting it as an issue for greater transparency. Note that code in this branch is likely to be very much in-progress and prone to bugs until I merge it into master.