#36 Better support for cutting two-page bookscans into separate pages

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I use briss a lot for cutting my bookscans with two pages per scan into separate pages. The only disadvantage is that I have to draw 4 squares manually for every pdf (2 squares for the even pages, 2 for the odd), since algorithm that detects the page size doesn't recognize double pages.

It would be great if the program would give more support for this kind of cropping. I can imagine the following possibilities:
- recognition of detect double pages resulting in suggestion for two copping areas per page.
- the possibility to save a cropping setting
- The option to turn off the distinction between even and odd pages, so that only two squares have to be drawn in this case.