PlotService: add converter from Plot to ImagePlus and Img

[maarzt]

ImageJ users (that use the new PlotService) will want to convert plots to Img and ImagePlus.
The converters to enable this should be part of imagej-legacy, as the conversion depends on ImagePlus.

This PR depends on scijava/scijava-ui-swing#43

[imagejan]

I'd suggest we support direct Plot => Img (or BufferedImage => Img) conversion in imagej-common so that we don't need to depend on ij.jar.

[haesleinhuepf]

I'd suggest you get this merged before another 4 years pass by.

[imagejan]

Hi @haesleinhuepf, what's up?

Sorry if I've been a bit too pressing. It's not urgent for me 😉

By the way, did you see that scijava/scijava-ui-swing#43 was effectively merged in April, and that PlotService is actively used by SNT? See also this forum topic Awesome, isn't it 😄

My suggestion above was really just to make sure we can also convert to Img when we don't have imagej-legacy on the class path. (Alright, I should open a new issue in imagej-common.) But it doesn't hurt having the converter here as well, of course.