HER-2040 ExtractorJS shouldExtract when content-type is application/json
new contrib subproject for extra generally useful modules not part of the main distribution
import Adam's ExtractorYoutubeFormatStream from its former home https://github.com/adam-miller/ExtractorYoutubeFormatStream
extractIndependently=true so that earlier ExtractorHTML extraction doesn't stop us from extracting here; also use java.net.URLDecoder
ExtractorYoutubeFormatStream.java
	Parse parameters instead of attempting to regex desired values
	Add priority itag list and extract limit

ExtractorYoutubeFormatStreamTest.java
	Test cases for extracting all videos and extracting single video
make ExtractorYoutubeFormatStream extend Extractor instead of ContentExtractor because we don't really want the extra stuff that ContentExtractor does
only extract urls that look like youtube watch pages
test crawl reveals generate_204 urls apparently not needed
implement itagPriority and extractLimit parameters
address HER-2042 - new annotation duplicate:uriAgnosticDigest for all url agnostic duplicates, whether written to warcs or not; stats consult this annotation so that duplicate/novel numbers are correct