Aral and Ian video links

Added the video links to Youtube
Video and slides buttons

Changed normal links to small buttons
Secondary button for videos

Added secondary button style to separate videos from slides
Video button optimization

On mobile the buttons had some issues: If the button text had 2 lines
of text, the line height was too high and the button after button
selector forced and indent on the second button in a new line which I
removed now.
Nico video link

Added Nicos talk link
Merge pull request #55 from asciidisco/videos

I merge the video button links for Aral, Ian and Nico now.