Block & tag support

Hi there,

I started from your LBYouTubeView repo because of the optimisations you implemented.
Great work!

So I've added 2 things to LBYouTubeExtractor:

1. Block- support (like in the original larcus94/LBYouTubeView repo).

2. Tag- support.
This is extremely useful if one would like to extract a bunch of YouTube URLs... let's say inside a loop?
Developers can tag the extractor and their tag will be returned in its delegate methods and/or blocks.

It would be cool if you could merge my changes and send a pull request to larcus94 ;-).
Or if you don't like it... let me know.

Thanks in advance and happy coding!