Add experimental timeline view

[matiaskorhonen]

Add an experimental timeline view of the conferences

Reason for Change

• There are a lot of upcoming conferences so visualising what's taking place when is a bit hard
• This also makes it easier to spot events that overlap

Changes

• Adds a Mermaid Gantt chart of the current year's events
• There's still work to be done here before this is ready for production, among other things:
  • [ ] Fix the chart colours
  • [ ] Fix the chart font
  • [ ] Self-host the mermaid JS file
  • [ ] Event name escaping is a bit hacky at the moment but I couldn't figure out a better way to do it with Liquid/Jekyll
  • [ ] Figure out if there's a better library to use for the chart

Minor

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