Switch the palette of 1bbp images if they appear to be negatives.
Images are forced to be output as png.
Extractor handles getting null image.

This happens if the image can't be decoded, eg is JPX encoded.
Added Browse folder button.
Ignores any pdf files in the pages folder.
Fixed a couple of bugs in checking for negative images.
Fix negative check to try to handle torn page corners.
Made install remove program entries for previous versions.