Zdeněk,
I am not sure what you are missing. If you want to add a new feature action to the WAB popup menu then you add a new class that extends jimu/BaseFeatureAction in the [install dir]\server\apps\[app#]\jimu.js\featureActions or if you want your featureAction only be added to the app when your widget is used then you follow the link posted earlier to add on to your widget like the AttributeTable/actions/ViewInAttributeTableFeatureAction.js