add libsonic as a submodule
cloned from https://github.com/lrusak/plugin.audio.subsonic/commit/ad830b67ddf88926e 12f75952e341d8d842cdb27
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cloned from https://github.com/lrusak/plugin.audio.subsonic/commit/ad830b67ddf88926e 12f75952e341d8d842cdb27