Download csv measurements template.

- Don't show csv tab when user not permitted or when no devices present.
Merge pull request #91 from MastodonC/feature/csv-template-download

Download csv measurements template.
prismatic schema for devices and sensors.
Add device / sensor validation to csv-upload.
Add validation of header.
Better schema defs.
Upgrade to kixi.pipe 0.17.8.
Implement data level authz.
More authorization work.
more data in status file.