Measurements have a cancelled_at column

[OAGr]

Measurements get a cancelled_at column. This will be manually accessed via the database to withdraw (remove) certain invalid or mistaken measurements, without actually deleting them.

TODO:

• Add an optional cancelled_at time column to measurements.
• If there is a time in the cancelled_at column, the aggregator should ignore it. It should basically be treated as deleted from aggregators.
• On the client, if a measurement is cancelled, it should show a "cancelled" tag, next to the "input text" (this isn't amazing, not sure where this should go).

The view to change this is here:

Use this view as the "tag" component.

[RomanGalochkin]

It looks like this screen now: