[yuvutu] Add new extractor

[drguildo]

Before submitting a pull request make sure you have:

• At least skimmed through adding new extractor tutorial and youtube-dl coding conventions sections
• Searched the bugtracker for similar pull requests

In order to be accepted and merged into youtube-dl each piece of code must be in public domain or released under Unlicense. Check one of the following options:

• I am the original author of this code and I am willing to release it under Unlicense
• I am not the original author of this code but it is in public domain or released under Unlicense (provide reliable evidence)

What is the purpose of your pull request?

• Bug fix
• Improvement
• New extractor
• New feature

---

Added an extractor for Yuvutu.

$ python test\test_download.py TestDownload.test_Yuvutu
[Yuvutu] 330: Downloading webpage
[Yuvutu] 330: Downloading webpage
[info] Writing video description metadata as JSON to: 330.info.json
[debug] Invoking downloader on 'http://cdn.yuvutu.com/prod/streams/330_carnalbliss.flv?nvb=20161007102807&nva=20161007202807&hash=0083873be750ddaf1b3f9'
[download] Destination: 330.flv
[download] 100% of 10.00KiB in 00:00
.
----------------------------------------------------------------------
Ran 1 test in 1.684s

OK

[dstftw]

These should be moved at places of their usage since they only used once.

[drguildo]

$ python test\test_download.py TestDownload.test_YuvutuUser
[YuvutuUser] 1072966: Downloading user page 1
[YuvutuUser] 1072966: Downloading user page 2
[YuvutuUser] 1072966: Downloading user page 3
[download] Downloading playlist: 1072966
[YuvutuUser] playlist 1072966: Collected 90 video ids (downloading 90 of them)
[download] Downloading video 1 of 90
--✂--
[download] Downloading video 90 of 90
[download] Finished downloading playlist: 1072966
.
----------------------------------------------------------------------
Ran 1 test in 3.354s

OK