WidgetStyle: add javadoc and new method

[imagejan]

While getStyleModifiers() is useful for things like "extensions:png/gif/bmp", this commit adds a new getStyleModifier() method that simply returns the suffix after the colon (:), for cases like "format:#0.001".

See also scijava/scijava-ui-swing#52.

[imagejan]

@ctrueden just saw your comment here: #384 (comment)

If we're free to change the API of WidgetStyle, we could consider a) changing the return type of getModifiers() from String[] to Set<String> or b) removing the getModifiers signature entirely.

Also, I'm still open to (re-)naming suggestions :-)

[imagejan]

@hinerm do you think this can be merged? Or alternatively, we can adapt the API introduced in #384, but I'm afraid there has been a release by now, so it would be a breaking API change (although no SciJava component was using it yet) ...

Anyhow, I think it would be good to get this done, so we can proceed with scijava/scijava-ui-swing#54 and scijava/scijava-ui-swing#56.

[imagesc-bot]

This pull request has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/save-one-tiff-projection-from-a-current-view-in-bdv/33965/28