Store state in local storage/db

**Is your feature request related to a problem? Please describe.**
> I automatically press F5 to render a preview. If I do that in the web interface, then my changes are lost.

**Describe the solution you'd like**
While F5 might be able to be supressed, I think the better approach would be to store the state in local storage. This way I don't interfere with the browsers refresh functionality.
