I have made the 2 tweaks to the code (config.json & LayerInfos.js).
Creating a new app results in the following view in the Widgets tab - I cannot "edit" the LocalLayer widget.
The LocalLayer widget shows up as "6"....when I click on it, it pops up the widget list....none of which are the LocalLayer widget
Sounds like you need to go to this url and follow the steps for setting up the widget
Because from the looks of it you have something wrong in the setup.
I went back and did a fresh "install" of WAB1.3, and made the appropriate changes to the 2 files - but this time I changed the config.js file in the "Default" app under the "predefined-apps" folder. My last attempt I only updated the config.js under the stemapp folder. I then created a new application and the widget showed up properly.