Liquid Bear / Atraci like behaviour

This pull request allows the user to define how the addon will work. Basically, the user can choose which site the addon uses as a media source. If the user chooses vk.com the addon will behave as before (like the liquid bear app). Choosing youtube, the addon will browse youtube for the song and play it right away (like the Atraci). Atraci is an open-source program for win/osx/linux that uses last.fm api combined with youtube. You can read more about it here: http://getatraci.net/.

It is working fine, however it seems there are some issues with the official youtube plugin at the moment (still a pull request left to be accepted in the oficial xbmc.org repository).

Cheers and keep it up