Use classnames instead of service IDs

[leofeyer]

This PR replaces the contao. service IDs with class names as recommended in Symfony 4.

TODO

• Also convert the private services
• Add aliases for the private services
• Check for ->getDefinition()->getClass(), which now returns null

[aschempp]

There's a looot of changes here. Before we review every file, am I correct that you did not add aliases for all current services? Because I think we should, regardless of whether they should have been used or not…
Also, can/should be add deprecated to the aliased services? Or is that even possible?

[leofeyer]

This PR has been closed as the concept does not really work for a bundle. All the fancy stuff such as service annotations or autowiring (which is what class names as service IDs is mainly for) work best in your app.

[aschempp]

I don't understand why that would not work in our bundle?