The client pings repeadedly for status updates

Add user id to visualizations

Fix user authentication decoding

Only temporary. Will be added again later on.

Allow empty widget name

Add owner validation

Removed adminLevel from users

Add missing simulator attribute in plot model

Simulations are the container for simulation models

Rename app.js back to server.js.

Rename server.js to app.js.
Add 404 and error handling middleware.

Add rows and columns to plot

Post routes create needed relationships when creating new entries.
The associated entires are deleted on deleting an entry (e.g. deleting a project
leads to deleting all visualizations and plots belonging to this project.

Add relationship from visualization to project.
Add plot-type attribute.

Change response on delete routes.