NowPlaying: Add support for embedded covers in vorbis files

[d3xMachina]

I suggest to implement the support for embedded covers in vorbis files.

To implement this feature the library "Taglib" needs to be updated since the version in Rainmeter does not have the support for pictures in Xiph comments. Then GetEmbedded() in Cover.cpp have to call TagLib::Ogg::XiphComment::pictureList() to get the cover of vorbis files.