Make partiness optional

[somewhatabstract]

With the ability to just animate or modify a source image, we might not always want to add the party palette.

I know, sacrilegious!

[gsmith077]

I'd like to chime in on this:

I recently used this tool to do a partial party-version of an image, where only a masked section was doing the rainbow animation. I used GIMP to create the mask and overlay.

It would be nice to have the option to do similar for a rotating or radiused image. There are also multiple examples (flag party parrots) where they have the animation without the rainbow.