Documentation of WebTester's underlying Concepts and Principles

[slu-it]

We need an in dept documentation / article about the underlying concepts and principles of WebTester 2.

It should cover the following topics:

• Why Interfaces instead of Classes?
• Composition through multiple inheritance over class hierarchy (traits)
• Design of Pages
• Design of Page Fragments
• Nesting of Pages and Page Fragments
• Which methods should be declared on which object