BUGFIX: textboxes broken, fixed. Turns out all strings are considered
lists, so my validation was defective. added flag to function.
BUGFIX: If checkbox "resize" deselected after setting several sizes, artscript
ingored it.
Added experimental support for image watermark Centered.

Set "wmimsrc" value in settings to an absolute path.
	/home/user/image.xxx
like this
	wmimsrc="/home/user/image.xxx"