Taxonomy demo has Java compilation errors

Build taxonomy demo as described at https://code.onehippo.org/cms-community-dev/hippo-plugin-taxonomy

First, you'll get:

[ERROR] /Users/niels/workspace/sandbox/screenshots/myproject/site/components/src/main/java/org/example/components/TaxonomyCategoryResult.java:[147,8] error: method does not override or implement a method from a supertype

After fixing that one, you get:

[ERROR] /Users/niels/workspace/sandbox/screenshots/myproject/cms/src/main/java/org/onehippo/taxonomy/demo/HideForAuthorCategoryFilter.java:[49,56] error: incompatible types: String cannot be converted to Group