Multicast: SSM support in the playlist interface

Source Specific Multicast requires the multicast group and the source IP to be specified. The format therfore is udp://@:

Currently the playlist GUI allows only for specifying the multicast group udp://@: and requires the syntax to be manually entered in the advanced options of the GUI.

Tested against 0.9.8 release on Win32 and Linux (Mac OSX unfortunately doesn't support IGMPv3/SSM in the current network stack).

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