Luftdatenpumpe

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- Improve EEA station processing
- Update "pflock" command to report if invocation failed
- Use HTTP POST when creating the InfluxDB datasource. Thanks, David.

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- Improve memory consumption
- Don't process non-float values

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- Mask observation values with magic number ``-99.99`` representing ``NaN``
values from SOS/IRCELINE, 3.

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- Update documentation for installing Grafana Worldmap Plugin
- Add Redis setup documentation re. 7. Thanks, David.
- Add PostgreSQL setup documentation re. 8. Thanks, David.
- Fix LDI historical data import, 10. Thanks, Wetter.

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- Update ``GRAFANA_URL`` in documentation
- Improve data wrangling robustness for luftdaten.info
- Acquire and process station list from EEA

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- Nothing changed