Youtube Online Check using Api

Hi,

I have tested my proposal from here: https://github.com/pyload/pyload/issues/163

It's is working pretty well.

It might be a better approach to actually parse the XML and not just "regexing" it.
One reason for doing this is: The api also provides the name of the video, that would make the parser more resistant against changes around the title on the website.

I would also suggest to split up the file a little more, that would make understanding a lot easier and it would be more modular.

Anyway hope this fix meets you standards, if it does and my proposals make sense to you guys, I would begin and make the changes.