Initial documentation for the examples
    - A .qdoc file for each example (no detailed docs yet)
    - A new group page 'examples-qtwinextras'
    - Add examples section to module index page
    - New TOC entry 'Examples' for the QCH file
    - Fix example path in .qdocconf

Change-Id: I2642e31e2eea361b47118b7b560d6c71d9780743
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>