add and use DEFAULT_LOCALE constant
configure embedded youtube video

- origin=www.getlantern.org (more secure)
- autohide=1 (hide player controls while watching)
- enablejsapi=1 (will use js api in the future to set captions track)
- rel=0 (don't show related videos at the end)
- showinfo=0 (don't show topbar with video title)
forgot "constants" dependency declaration

should have gone in 0238849b5
first pass at responsive video