Include button to delete dummy default data

On first start the app should populate with some dummy default data to show how it can be used. Include a button to easily delete everything and start from scratch.

Maybe the button should only be displayed the first few times the app is started or something.

Trace where first-start dummy data is populated and where the app's existing controls are rendered. Determine how the frontend can request deletion of all dummy data and how the backend handles that request. Done means a user can start with the sample data, use a visible button to remove it, and begin from an empty state.

Written by the indexing model from the issue text.