video: add video rewriting use vidrw client side and youtube-dl on the server

add vi_ modifier:
-on record, gets video_info from youtube-dl, sends to proxy,
if any, via PUTMETA to create metadata record
-on playback, fetches special metadata record with video info and
returns to client as json
-vidrw script: fetches video info, if any, and attempts to replace
iframe and embed tags (so far) which are videos
wombat: export extract_url function, fix spaces and use object instance
semantics
setup: add youtube_dl as dependency
rewrite: add call to _live_rewrite_headers to get correct headers for
proxy on video info
wombat: add wombat class to window
video: add video rewriting use vidrw client side and youtube-dl on the server

add vi_ modifier:
-on record, gets video_info from youtube-dl, sends to proxy,
if any, via PUTMETA to create metadata record
-on playback, fetches special metadata record with video info and
returns to client as json
-vidrw script: fetches video info, if any, and attempts to replace
iframe and embed tags (so far) which are videos
wombat: export extract_url function, fix spaces and use object instance
semantics
setup: add youtube_dl as dependency
rewrite: add call to _live_rewrite_headers to get correct headers for
proxy on video info
wombat: add wombat class to window
vidrw: work on yt rewrite
cache: move cache wrappers to seperate cache.py in framework from
proxy_resolvers
range cache: and buffering cache for serving range requests, intended
for videos but not only. full response cached in temp file and range
requests served from cache, still experimental
need to add deletion.
youtube_dl: wrap youtube-dl import due to youtube-dl HTMLParser regex
bug
tests: add test for vi_ handler
Merge branch 'video' of https://github.com/ikreymer/pywb into video
wombat: add generic setAttribute override for href and src, Image object
override, src prop rewrite
rewrite: add support for srcset rewriting for img tag
banner insert: extra check for document.body before adding banner
video: work on domain-specific range cache rewrites
Merge branch 'develop' into video
video work: live rewrite pings proxy with full rewrite, proxies direct
range request
reorg rangecache to support is_range() check, yt-specific logic
(experimental)
wombat: add date override (experimental)
bump tentative version to 0.7.0!
yt replays work with native player! (though still issues remain)
rangecache: always bound range, set default bound of 16384
wombat: work on date override, disable for now
head_insert: check for wombat not being inited to avoid undef error
Merge branch 'develop' into video
rangecache: don't redirect when using range header, don't cache non-200
responses
add flowplayer 3.2 for flash fallback
rangecache: use tmp dir for cache and delete on exit