[techtalks] Add support for authentication

[markostam]

Make sure you are using the latest version: run youtube-dl --version and ensure your version is 2016.09.15. If it's not read this FAQ entry and update. Issues with outdated version will be rejected.

• I've verified and I assure that I'm running youtube-dl 2016.09.15

Before submitting an issue make sure you have:

• At least skimmed through README and most notably FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones

What is the purpose of your issue?

• Bug report (encountered problems with youtube-dl)
• Site support request (request for adding support for a new site)
• Feature request (request for a new functionality)
• Question
• Other

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$ youtube-dl -v -u PRIVATE -p PRIVATE http://techtalks.tv/talks/lecture-sep-14th-2/61647
[debug] System config: []
[debug] User config: []
[debug] Command-line args: ['-v', '-u', 'PRIVATE', '-p', 'PRIVATE', 'http://techtalks.tv/talks/lecture-sep-14th-2/61647']
[debug] Encodings: locale UTF-8, fs utf-8, out UTF-8, pref UTF-8
[debug] youtube-dl version 2016.09.15
[debug] Python version 3.5.2 - Darwin-15.6.0-x86_64-i386-64bit
[debug] exe versions: ffmpeg 2.8.6, ffprobe 2.8.6
[debug] Proxy map: {}
[generic] 61647: Requesting header
[redirect] Following redirect to http://techtalks.tv/account/login/?next=/talks/lecture-sep-14th-2/61647/
[generic] 61647: Requesting header
WARNING: Falling back on generic information extractor.
[generic] 61647: Downloading webpage
[generic] 61647: Extracting information
ERROR: Unsupported URL: http://techtalks.tv/account/login/?next=/talks/lecture-sep-14th-2/61647/
Traceback (most recent call last):
  File "/usr/local/bin/youtube-dl/youtube_dl/YoutubeDL.py", line 694, in extract_info
    ie_result = ie.extract(url)
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/common.py", line 347, in extract
    return self._real_extract(url)
  File "/usr/local/bin/youtube-dl/youtube_dl/extractor/generic.py", line 2393, in _real_extract
    raise UnsupportedError(url)
youtube_dl.utils.UnsupportedError: Unsupported URL: http://techtalks.tv/account/login/?next=/talks/lecture-sep-14th-2/61647/