Add Coffee example

This example shows how to split logic from declarative
the QML and how to design an application using
Qt Quick Designer.

Change-Id: I9c20aa26fcc269530036a4f67aed5a84ba1aa1fd
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>
Reviewed-by: Petref Saraci <petref.saraci@qt.io>