Rename "slot" to "session" for clearity
Enhance session detail with youtube and slides, list all speakers nicely
Merge branch 'improvements'

Conflicts:
	data/2013/agenda.json
Add youtube videos to session page
Add description and slides placeholder to session
Add link to session to whole block, add icons for showing the existence of slides and/or video
All speaker images should be square
Add speaker images to session page, use placeholder if not exists
Optimize some descriptions
Optimize display of speaker list and add some more fancy effects