TODO
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Basic
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- set start/end date of the analysis (the end date defaults to "now")
- add/remove *pattern* entries, each consists of:

  - name (label)
  - calendar name (or regex to match calendar name)
  - regex to match title ("*" by default)
  - regex to match location
  - regex to match description
  - time filter (for filtering out short/long events)

- analyze button to show the charts

Advanced
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- listen to calendar updates
- cache the result and make deltas