Doc: Create documentation structure for Qt Mac Extras

Create documentation structure for the module
    - Module qdocconf
    - Documentation pages for module index, namespace/classes,
      examples (not much content yet)

Other doc-related changes
    - Enable running 'make docs' on all platforms
    - Move examples under examples/macextras for a clean
      installing to QT_INSTALL_EXAMPLES
    - Ensure documented classes use correct \inmodule and
      \since commands
    - Add \namespace QtMac
    - Other minor fixes

Change-Id: I1376d68fcd7ab324a5d3355f1d15914092900e5b
Reviewed-by: Morten Johan Sørvig <morten.sorvig@digia.com>