Update YoutubeExtractor

This fixes some of the issues with YouTube
Release of version 2.2.1
Implement a basic Drag & Drop functionality to drag songs into the playlist
Updated YoutubeExtractor
Add Drag & Drop for direct YouTube links

Fixes #10
Verify that the YouTube URL is an actual URL
Add some tests for the DirectYoutubeViewModel
Check against null
Implemented Drag & Drop moving inside the playlist