Bug fixes and signed with certificate

Executables are now signed with a certificate, should prevent Windows warning messages.

The following has been fixed:

- Imported image file locked while in use

- BMP image import with red and blue swapped around

- Exported text version includes 256 color count instead of actual color count

- Exported text version has space before colon of description

- Exported GIMP version includes 256 color count instead of actual color count

- Exported GIMP version has spaces before colon of each field

- Exported JASC-PAL version includes 256 color count instead of actual color count