[API] Add new GetMetaData Media Object API

- Add a new method GetMetaData to the org.gnome.UPnP.MediaObject2 interface to allow
the retrieval of the Meta data information of an object in DIDL-Lite XML format.
- MediaConsole python test app updated.
- Doc updated.
- Fix issue https://github.com/01org/dleyna-server/issues/25

Signed-off-by: Christophe Guiraud <christophe.guiraud@intel.com>