read orientation from file (via vips) and several improvements to preview loading/creating, needs revision and tuning...

Signed-off-by: Alex A. Naanou <alex.nanou@gmail.com>
some tuning, cleaning and refactoring...

Signed-off-by: Alex A. Naanou <alex.nanou@gmail.com>
moved preview processing to loadRawDir(...), more tweaking...

Signed-off-by: Alex A. Naanou <alex.nanou@gmail.com>