Improve UX of rotated crop

[SafariMonkey]

Description

• ROI region is cropped at the same time as rotation, not before, so the crop doesn't cut into the rotated ROI
  • Filling the background is skipped if the crop is entirely within the camera image, and the image is warped with transparency enabled and then filled based on the average colors of non-transparent pixels otherwise.
• Make ROI widget rotate the image, optionally with padding so the widget stays the same size as it rotates
  • The crop is limited to the axis-aligned bounding box (AABB) of the image corners, to make it easier to not waste any rows or columns.
• Add a crosshair to the ROI widget (with some slightly sneaky access of the underlying tkinter to set the dashed line property)

Checklist

• I accept the CLA.