Backfill precise Withings sleep data

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