improve embedding youtube videos

make regex detecting youtube videos more flexible
it now matches both:
    http://youtu.be/{video id}
and:
    http://www.youtube.com/watch?v={video id}
    http://m.youtube.com/watch?v={video id}
add vine videos in twitter feed
fix CSS syntax errors
Merge remote-tracking branch 'origin/css-fixes'
Merge remote-tracking branch 'origin/youtube-fix'
Merge remote-tracking branch 'origin/vine'