This is a skeleton of OpenRefine extension for Wikimedia Commons, in the form of an independent Maven project. It works with OpenRefine 3.6+.
Run
mvn package
This creates a zip file in the target folder, which can then be installed in OpenRefine.
To avoid having to unzip the extension in the corresponding directory every time you want to test it, you can also use another set up: simply create a symbolic link from your extensions folder in OpenRefine to the local copy of this repository. You will still need to restart OpenRefine every time you make changes.