New CSS component: Toast notification

[devmount]

Is your feature request related to a problem? Please describe.
There should be a possibility to show toast notifications to provide feedback if something was successful or not.

Describe the component you'd like for that problem

• Introducing a new class .toast
• Providing notifications in neutral, accent, positive and negative variant
• Provide 4 positions (each screen corner)

Additional context
For content embedded messages use .callout(see #19)