dleyna: DLNA service discovery using dLeyna

see: https://01.org/dleyna

dLeyna is an umbrella project hosting a number of middleware components
designed to make it easy for developers to integrate DLNA functionality
into their applications.

This SD module connects to dleyna through D-Bus in order to discover
available DLNA UPnP A/V devices and browse their content.
dleyna: Check if dLeyna is present on the bus

/!\ Should be removed in favor of dbus activation
dleyna: Start a probing thread once the module is initialized
dleyna: Call GetServers in the probe thread
dleyna: Update comment
dleyna: Read the GetServers reply when probing for devices
dleyna: iterate through the results of GetServers
dleyna: fix copyright notice
dleyna: Retrieve the media servers' friendly names
dleyna: Do not leak dbus messages and check arg types
dleyna: Move the string property marshalling code to a separate function
dleyna: Add the dLeyna media server object data structure
dleyna: Add a location field to the dleyna server data structure

Add psz_location, which contains the URI of the XML device description
document.
dleyna: Use org.freedesktop.DBus.Properties.GetAll

Read all media server properties at once using the GetAll method of the
Properties DBus interface and fill the media server data structure with
the results.