Improvements to calculated datasets

- Use hourly_rollups.
- Improve datasets API and UI.
- Insert dirty dates for calc datasets.
- Fix failing test, field calcs using raw data.
- Don't quantise.
- Improvements to UI and fix to date ranges.
- Fixed periods.
Add migration script.
Act on @otfrom's comments.
Merge pull request #424 from MastodonC/feature/calc-datasets-using-rollups

Calculated datasets using rollups