Toshaan Bharvani 655d367954 update events
- add all summit events from 2015
  updated from old website
- update layout with better pointers and bullets
- change colors to be a more contrast for visibility
- update eventdates with from and till
  now able to have multiple dates
  listing is based on from date

Signed-off-by: Toshaan Bharvani <toshaan@vantosh.com>
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_index.md update events
fosdem21.md update events
fosdem22.md update events
openpowersummit15.md update events
openpowersummit15china.md update events
openpowersummit16.md update events
openpowersummit16china.md update events
openpowersummit16eu.md update events
openpowersummit18eu.md update events
openpowersummit18us.md update events
openpowersummit19eu.md update events
openpowersummit19na.md update events
openpowersummit20.md update events
openpowersummit21.md update events
openpowersummit22.md update events
openpowersummit23.md update events