[BR] Add "BR" extractor

Extractor for videos from the Bayerischer Rundfunk Mediathek[1]. Currently only
supports videos. Audio and podcasts do not work yet with this extractor.

1: http://br.de/mediathek
[BR] Add basic test
Merge remote-tracking branch 'soult/br'
[br] Simplify
Credit @soult for br
[videobam] Add support for videobam.com (Closes #2411)
[f4m] Clean up
Fix imports
[videobam] Set age_limit to 18

From [their ToS](http://videobam.com/terms): "User must be eighteen 18[sic] years of age or older to use or access this web site."
release 2014.02.22.1
[vine] Fix uploader extraction
[breakcom] Fix info json extraction
[breakcom] Fix error when calling _search_regex

I passed `’webpage’` instead of the variable `webpage`.
Add one more format to unified_strdate
[vine] Extract more metadata and support low format
[youtube:playlist] Fix mixes extraction (fixes #2444)
[normalboots] Fix video url extraction
[normalboots] Modernize and simplify
[youtube] Fix mix video regex

Attributes' order in <li> is arbitrary and changes every time playlist
page is fetched, so we can't rely on `data-index` to be before
`data-video-username`.