Introduce tagging

[SteffiPeTaffy]

• tagging
  • series (craft conf, jsconf, devoxx, euroclojure, …)
  • category (tw presents, meetup, …)
  • topics (buzzwords: agile, javascript, …)
  • roles (dev, devops, …)
  • tags (inspiring, entertaining, informative, …)
  • experience levels (rookie, beginner, intermediate, …)

[SteffiPeTaffy]

Right now, we decided to go with #tags in the description only.