[Property] Don't return empty properties in GetAll

Remove various empty properties from Item and Container.

Signed-off-by: Ludovic Ferrandis <ludovic.ferrandis@intel.com>
[Property] Support for new "Error" property

Add a new 'Error' property, used by BrowseObjects for instance.
Error is a dictionary with 2 entries:
ID: u -> Numeric error code
Message: s -> Error message

Signed-off-by: Ludovic Ferrandis <ludovic.ferrandis@intel.com>
[Filtering] Use generic filtering for GetAll

Task GetAll has a field member 'filter_mask'.
This task and field are used by other methods, but not by GetAll properties.
GetAll parsing function used directly DLS_UPNP_MASK_ALL_PROPS constant in the code.

This will prevent to reuse the GetAll parsing function with another filter mask.

Initialize filter_mask to DLS_UPNP_MASK_ALL_PROPS in GetAll method and use
filter_mask in the GetAll parsing function.

Signed-off-by: Ludovic Ferrandis <ludovic.ferrandis@intel.com>
[API] Add new BrowseObjects API

Add new BrowseObjects API in MediaDevice interface

Fix issue #114: <https://github.com/01org/dleyna-server/issues/114>

Signed-off-by: Ludovic Ferrandis <ludovic.ferrandis@intel.com>