Smart layout switching

[kirillt]

When we pivot images by 90°, we alternate the layout from portrait to landscape, and vice versa. This ensures no data is lost.

This concept could be extended to any rotation angle. The goal is to keep image data loss to a minimum. That is, reducing the area of image portions that fall outside the image boundaries. We can achieve this by switching layouts not just at a straight 90°, but also for any angle within the 45° — 135° and 225° — 315° ranges.

• Rotation mode should include checkbox [use_smart_switching]

• When the rotation angle falls within the ranges specified above:
  * if [use_smart_switching] is checked, the layout changes automatically
  * if [use_smart_switching] is unchecked, a [switch_layout] button appears
  * pressing [switch_layout] changes the layout

[kirillt]

Implemented in #82