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.

Add cors package.
Add /users/me route to identify from auth token.

Add UML class and use-case diagram (StarUML application).
Add admin user from config if no admin user found.

The higher the level, the more rights a user has
Fix error not checking password in authenication

User passwords are stored with bcrypt hash & salt.
The authentication token is stored in the 'x-access-token' header.

For tests open mongodb port and access directly (without docker)