Group fill property

[timothystone]

group currently only supports the icon and color properties. background and opacity would be a welcome additions. We often want to provide more visual contrast in nested groups.

I might be able to provide a PR, but my Java is pretty rusty. You may cringe. 😉

[simonbrowndotje]

Support for this was added a few weeks ago (d02ddb4) and will be in the next release. 🙂