Add watermark support

[ribtoks]

Thank you for developing Gallery Deluxe! (it was the only gallery that "just worked" for me).

Would be great if during/after generation, gallery supported applying a .png watermark on top of images.

Why it has to be done on the gallery level and not at originals level is that tiny previews should not have a watermark, while when user clicks to see the larger picture - it should have one.

[bep]

Yea, that sounds like a good idea.

[ribtoks]

Wow, I couldn't imagine that it can be added so fast. Thank you! Already migrated from my bash script with composite from ImageMagick and it works!