Fixed a possible null-pointer exception in DNG_DefaultCropOrigin and DNG_DefaultCropSize resulting from an uninitialized array.

Added a 16-bit, big endian test pic
Added support for the "FillOrder"-Tag, which describes in which order pixels are packed into bytes (for depths != 8, 16 or 32)
Buffered the BitsPerSample-Value in a member variable, because it's used often
Added support for images with 8, 16 or 32-bit color depth. 32 bit will not really work correctly because I used ints everywhere which can only store 31 bit unsigned...