We don't show a graph summary anymore just the last available data in the collection.

We don't need this to be so complex anymore.

getValueSelected and getLabelSelected just call getValue and getLabel now.
Add tests for label summary
Fix scoping issue due to refactor.

Check for falsey models instead of strictly null.
Merge pull request #687 from alphagov/bugfix/volumetrics-number

Bugfix/volumetrics number