Backfill precise Withings sleep data

[Felix Krause]

Looks like Withings actually properly handles time zones and supports the "fell asleep" and "woke up at"

We could then render all of this per day via https://echarts.apache.org/examples/en/editor.html?c=data-transform-aggregate

Or we group it by factor (e.g. city) and then render the sleep times like https://echarts.apache.org/examples/en/editor.html?c=data-transform-aggregate