Add a persistence data viewer/manager

[florian-h05]

The problem

When working with persistence data, it might be useful to easily see which Items are available in persistence and what data is persisted for them.
It would be even greater if one could delete data from persistence through the admin part of the UI.

Your suggestion

Implement something like https://github.com/5iver/PersistenceViewer in Main UI and extend it with some management capabilities.