When developing new custom widgets the widget/theme development work flow I use for all my work is this.1. Copy the [install dir]\client\stemapp\widgets\samplewidgets\CustomWidgetTemplate folder to the stemapp widget folder and rename it to your custom widgets name.
2. Open the manifest.json and change the name property to the exact name of the widget folder from step one.
3. I now work on changing the icon and some basics of the widget.
4. Now I create a new app (normally the app will be named the same as my custom widgets name) and will see that my new custom widget is a choice in the widget choices.
5. Add my custom widget to the new app.
6. Now I do ALL my development in the [install dir]\server\apps\[app #]\widgets\my custom widget name folder.
7. Once I am done will my development I copy the widget folder back into the stemapp widgets folder so that new apps will use the completed widget code.