Log to an external logger (fixes #1810)

Sadly applications using youtube-dl's python sources can't directly
access it's log stream. It's pretty much limited to stdout and stderr
only.

It should log to logging.Logger instance passed to YoutubeDL's params
dictionary.
Add support for niconico
Merge remote-tracking branch 'iTaybb/master'
Simplify logger code(#1811)
Merge remote-tracking branch 'takuya0301/niconico'
[niconico] Simplify and make work with old Python versions

The website requires SSLv3, otherwise it just times out during SSL negotiation.