A better fix for csv downloads.

Fixes #406
Merge pull request #473 from MastodonC/feature/fix-csv-measurements-download

A better fix for csv downloads.
Introduce sensor_id.

- Update calculations.
- Store sensor_id in datasets.
- Update datasets API and UI to support sensor_id.
- Make dataset name editable.
- Update uploads and downloads with sensor_id.
- Update measurements API to support sensor_id.
- Update devices API.
Changes as per @otfrom's comments.