NEW FEATURE: customize cropping alignment for individual photos

When we were collecting feedbacks for version 1, quite a few users requested for allowing them to customize the cropping alignment of individual photos. However, we couldn't figure out how to achieve this without introducing some complicated interface.

In V2 we designed a new interface to show how the cropped image will be different from the original one. The idea is to use 2 blocks of transluscent bars to indicate which part will be cropped off. This gave us a new idea of how to solve the exact interface issue. We added some codes to allow the user to drag and move the clear part of the preview image to adjust the cropping alignment. The result is fantastic. Most of the user can figure out how to do it without any instruction.