1.5 Add option to watermark location

[wbnp]

Add Bottom center as an option in "Where to place watermark".

[Αndré]

Valid feature request imo. But then we should also add options like top/left/right + center. Cannot go to cpg1.5.x because of missing language strings.

[wbnp]

Actually "Top left" and "Top right" are already included so maybe all that would be needed are "Top center" and "Bottom center".